Fix warnings

Bumps [mio](https://github.com/tokio-rs/mio) from 0.8.10 to 0.8.11.
- [Release notes](https://github.com/tokio-rs/mio/releases)
- [Changelog](https://github.com/tokio-rs/mio/blob/master/CHANGELOG.md)
- [Commits](https://github.com/tokio-rs/mio/compare/v0.8.10...v0.8.11)

---
updated-dependencies:
- dependency-name: mio
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.editorconfig

@@ -0,0 +1,8 @@
+root = true
+
+[*]
+insert_final_newline = true
+
+[*.rs]
+indent_size = 4
+indent_style = space

.github/workflows/test.yml

@@ -13,7 +13,7 @@ env:
 
 jobs:
   rustfmt:
-    name: rustfmt / nightly-2022-02-11
+    name: rustfmt / nightly-2023-06-22
     runs-on: ubuntu-latest
 
     steps:
@@ -22,7 +22,7 @@ jobs:
 
       - name: Install rust
         run: |
-          rustup default nightly-2022-02-11
+          rustup default nightly-2023-06-22
           rustup component add rustfmt
 
       - name: cargo fmt
@@ -52,17 +52,11 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v2
 
-      - name: Setup cache
-        uses: actions/cache@v2
-        with:
-          path: |
-            ~/.cargo/registry
-            ~/.cargo/git
-            target
-          key: ${{ runner.os }}-cargo-check
-
       - name: Install rust
         run: rustup update --no-self-update stable
+
+      - name: Setup cache
+        uses: Swatinem/rust-cache@v2
       
       - name: Install cargo hack
         run: cargo install cargo-hack --debug
@@ -81,27 +75,21 @@ jobs:
             rust: stable
           - name: beta
             rust: beta
-          - name: 1.56.0
-            rust: 1.56.0
+          - name: '1.70'
+            rust: '1.70'
 
     steps:
       - name: Checkout
         uses: actions/checkout@v2
 
-      - name: Setup cache
-        uses: actions/cache@v2
-        with:
-          path: |
-            ~/.cargo/registry
-            ~/.cargo/git
-            target
-          key: ${{ runner.os }}-cargo-test-${{ matrix.rust }}
-
       - name: Install rust
         run: |
           rustup default ${{ matrix.rust }}
           rustup update --no-self-update ${{ matrix.rust }}
 
+      - name: Setup cache
+        uses: Swatinem/rust-cache@v2
+
       - name: Install postfix  
         run: |
           DEBIAN_FRONTEND=noninteractive sudo apt-get update
@@ -124,15 +112,24 @@ jobs:
       - name: Install dkimverify
         run: sudo apt -y install python3-dkim
 
+      - name: Work around early dependencies MSRV bump
+        run: |
+          cargo update -p anstyle --precise 1.0.2
+          cargo update -p clap --precise 4.3.24
+          cargo update -p clap_lex --precise 0.5.0
+
       - name: Test with no default features
         run: cargo test --no-default-features
 
       - name: Test with default features
         run: cargo test
 
-      - name: Test with all features
-        run: cargo test --all-features
+      - name: Test with all features (-native-tls)
+        run: cargo test --no-default-features --features async-std1,async-std1-rustls-tls,boring-tls,builder,dkim,file-transport,file-transport-envelope,hostname,mime03,pool,rustls-native-certs,rustls-tls,sendmail-transport,smtp-transport,tokio1,tokio1-boring-tls,tokio1-rustls-tls,tracing
   
+      - name: Test with all features (-boring-tls)
+        run: cargo test --no-default-features --features async-std1,async-std1-rustls-tls,builder,dkim,file-transport,file-transport-envelope,hostname,mime03,native-tls,pool,rustls-native-certs,rustls-tls,sendmail-transport,smtp-transport,tokio1,tokio1-native-tls,tokio1-rustls-tls,tracing
+
 #  coverage:
 #    name: Coverage
 #    runs-on: ubuntu-latest

.gitignore

@@ -4,4 +4,3 @@
 lettre.sublime-*
 lettre.iml
 target/
-/Cargo.lock

CHANGELOG.md

@@ -1,5 +1,195 @@
+<a name="v0.11.4"></a>
+### v0.11.4 (2024-01-28)
+
+#### Bug fixes
+
+* Percent decode credentials in SMTP connect URL ([#932], [#934])
+* Fix mimebody DKIM body-hash computation ([#923])
+
+[#923]: https://github.com/lettre/lettre/pull/923
+[#932]: https://github.com/lettre/lettre/pull/932
+[#934]: https://github.com/lettre/lettre/pull/934
+
+<a name="v0.11.3"></a>
+### v0.11.3 (2024-01-02)
+
+#### Features
+
+* Derive `Clone` for `FileTransport` and `AsyncFileTransport` ([#924])
+* Derive `Debug` for `SmtpTransport` ([#925])
+
+#### Misc
+
+* Upgrade `rustls` to v0.22 ([#921])
+* Drop once_cell dependency in favor of OnceLock from std ([#928])
+
+[#921]: https://github.com/lettre/lettre/pull/921
+[#924]: https://github.com/lettre/lettre/pull/924
+[#925]: https://github.com/lettre/lettre/pull/925
+[#928]: https://github.com/lettre/lettre/pull/928
+
+<a name="v0.11.2"></a>
+### v0.11.2 (2023-11-23)
+
+#### Upgrade notes
+
+* MSRV is now 1.70 ([#916])
+
+#### Misc
+
+* Bump `idna` to v0.5 ([#918])
+* Bump `boring` and `tokio-boring` to v4 ([#915])
+
+[#915]: https://github.com/lettre/lettre/pull/915
+[#916]: https://github.com/lettre/lettre/pull/916
+[#918]: https://github.com/lettre/lettre/pull/918
+
+<a name="v0.11.1"></a>
+### v0.11.1 (2023-10-24)
+
+#### Bug fixes
+
+* Fix `webpki-roots` certificate store setup ([#909])
+
+[#909]: https://github.com/lettre/lettre/pull/909
+
+<a name="v0.11.0"></a>
+### v0.11.0 (2023-10-15)
+
+While this release technically contains breaking changes, we expect most projects
+to be able to upgrade by only bumping the version in `Cargo.toml`.
+
+#### Upgrade notes
+
+* MSRV is now 1.65 ([#869] and [#881])
+* `AddressError` is now marked as `#[non_exhaustive]` ([#839])
+
+#### Features
+
+* Improve mailbox parsing ([#839])
+* Add construction of SMTP transport from URL ([#901])
+* Add `From<Address>` implementation for `Mailbox` ([#879])
+
+#### Misc
+
+* Bump `socket2` to v0.5 ([#868])
+* Bump `idna` to v0.4, `fastrand` to v2, `quoted_printable` to v0.5, `rsa` to v0.9 ([#882])
+* Bump `webpki-roots` to v0.25 ([#884] and [#890])
+* Bump `ed25519-dalek` to v2 fixing RUSTSEC-2022-0093 ([#896])
+* Bump `boring`ssl crates to v3 ([#897])
+
+[#839]: https://github.com/lettre/lettre/pull/839
+[#868]: https://github.com/lettre/lettre/pull/868
+[#869]: https://github.com/lettre/lettre/pull/869
+[#879]: https://github.com/lettre/lettre/pull/879
+[#881]: https://github.com/lettre/lettre/pull/881
+[#882]: https://github.com/lettre/lettre/pull/882
+[#884]: https://github.com/lettre/lettre/pull/884
+[#890]: https://github.com/lettre/lettre/pull/890
+[#896]: https://github.com/lettre/lettre/pull/896
+[#897]: https://github.com/lettre/lettre/pull/897
+[#901]: https://github.com/lettre/lettre/pull/901
+
+<a name="v0.10.4"></a>
+### v0.10.4 (2023-04-02)
+
+#### Misc
+
+* Bumped rustls to 0.21 and all related dependencies ([#867])
+
+[#867]: https://github.com/lettre/lettre/pull/867
+
+<a name="v0.10.3"></a>
+### v0.10.3 (2023-02-20)
+
+#### Announcements
+
+It was found that what had been used until now as a basic lettre 0.10
+`MessageBuilder::body` example failed to mention that for maximum
+compatibility with various email clients a `Content-Type` header
+should always be present in the message.
+
+##### Before
+
+```rust
+Message::builder()
+  // [...] some headers skipped for brevity
+  .body(String::from("A plaintext or html body"))?
+```
+
+##### Patch
+
+```diff
+ Message::builder()
+   // [...] some headers skipped for brevity
++  .header(ContentType::TEXT_PLAIN) // or `TEXT_HTML` if the body is html
+   .body(String::from("A plaintext or html body"))?
+```
+
+#### Features
+
+* Add support for rustls-native-certs when using rustls ([#843])
+
+[#843]: https://github.com/lettre/lettre/pull/843
+
+<a name="v0.10.2"></a>
+### v0.10.2 (2023-01-29)
+
+#### Upgrade notes
+
+* MSRV is now 1.60 ([#828])
+
+#### Features
+
+* Allow providing a custom `tokio` stream for `AsyncSmtpTransport` ([#805])
+* Return whole SMTP error message ([#821])
+
+#### Bug fixes
+
+* Mailbox displays wrongly when containing a comma and a non-ascii char in its name ([#827])
+* Require `quoted_printable` ^0.4.6 in order to fix encoding of tabs and spaces at the end of line ([#837])
+
+#### Misc
+
+* Increase tracing ([#848])
+* Bump `idna` to 0.3 ([#816])
+* Update `base64` to 0.21 ([#840] and [#851])
+* Update `rsa` to 0.8 ([#829] and [#852])
+
+[#805]: https://github.com/lettre/lettre/pull/805
+[#816]: https://github.com/lettre/lettre/pull/816
+[#821]: https://github.com/lettre/lettre/pull/821
+[#827]: https://github.com/lettre/lettre/pull/827
+[#828]: https://github.com/lettre/lettre/pull/828
+[#829]: https://github.com/lettre/lettre/pull/829
+[#837]: https://github.com/lettre/lettre/pull/837
+[#840]: https://github.com/lettre/lettre/pull/840
+[#848]: https://github.com/lettre/lettre/pull/848
+[#851]: https://github.com/lettre/lettre/pull/851
+[#852]: https://github.com/lettre/lettre/pull/852
+
+<a name="v0.10.1"></a>
+### v0.10.1 (2022-07-20)
+
+#### Features
+
+* Add `boring-tls` support for `SmtpTransport` and `AsyncSmtpTransport`. The latter is only supported with the tokio runtime. ([#797]) ([#798])
+* Make the minimum TLS version configurable. ([#799]) ([#800])
+
+#### Bug Fixes
+
+* Ensure connections are closed on abort. ([#801])
+* Fix SMTP dot stuffing. ([#803])
+
+[#797]: https://github.com/lettre/lettre/pull/797
+[#798]: https://github.com/lettre/lettre/pull/798
+[#799]: https://github.com/lettre/lettre/pull/799
+[#800]: https://github.com/lettre/lettre/pull/800
+[#801]: https://github.com/lettre/lettre/pull/801
+[#803]: https://github.com/lettre/lettre/pull/803
+
 <a name="v0.10.0"></a>
-### v0.10.0 (unreleased)
+### v0.10.0 (2022-06-29)
 
 #### Upgrade notes
 
@@ -29,6 +219,7 @@ Several breaking changes were made between 0.9 and 0.10, but changes should be s
 * Refactor `TlsParameters` implementation to not expose the internal TLS library
 * `FileTransport` writes emails into `.eml` instead of `.json`
 * When the hostname feature is disabled or hostname cannot be fetched, `127.0.0.1` is used instead of `localhost` as EHLO parameter (for better RFC compliance and mail server compatibility)
+* The `sendmail` and `file` transports aren't enabled by default anymore.
 * The `new` method of `ClientId` is deprecated
 * Rename `serde-impls` feature to `serde`
 * The `SendmailTransport` now uses the `sendmail` command in current `PATH` by default instead of
@@ -53,7 +244,7 @@ Several breaking changes were made between 0.9 and 0.10, but changes should be s
 * Update `hostname` to 0.3
 * Update to `nom` 6
 * Replace `log` with `tracing`
-* Move CI to Github Actions
+* Move CI to GitHub Actions
 * Use criterion for benchmarks
 
 <a name="v0.9.2"></a>

CONTRIBUTING.md

@@ -1,6 +1,6 @@
 ## Contributing to Lettre
 
-The following guidelines are inspired from the [hyper project](https://github.com/hyperium/hyper/blob/master/CONTRIBUTING.md).
+The following guidelines are inspired by the [hyper project](https://github.com/hyperium/hyper/blob/master/CONTRIBUTING.md).
 
 ### Code formatting
 

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "lettre"
 # remember to update html_root_url and README.md (Cargo.toml example and deps.rs badge)
-version = "0.10.0-rc.6"
+version = "0.11.4"
 description = "Email client"
 readme = "README.md"
 homepage = "https://lettre.rs"
@@ -11,7 +11,7 @@ authors = ["Alexis Mousset <contact@amousset.me>", "Paolo Barbolini <paolo@paolo
 categories = ["email", "network-programming"]
 keywords = ["email", "smtp", "mailer", "message", "sendmail"]
 edition = "2021"
-rust-version = "1.56"
+rust-version = "1.70"
 
 [badges]
 is-it-maintained-issue-resolution = { repository = "lettre/lettre" }
@@ -19,33 +19,37 @@ is-it-maintained-open-issues = { repository = "lettre/lettre" }
 maintenance = { status = "actively-developed" }
 
 [dependencies]
-idna = "0.2"
-once_cell = "1"
+chumsky = "0.9"
+idna = "0.5"
 tracing = { version = "0.1.16", default-features = false, features = ["std"], optional = true } # feature
 
 # builder
 httpdate = { version = "1", optional = true }
 mime = { version = "0.3.4", optional = true }
-fastrand = { version = "1.4", optional = true }
-quoted_printable = { version = "0.4", optional = true }
-base64 = { version = "0.13", optional = true }
-regex = { version = "1", default-features = false, features = ["std", "unicode-case"] }
-email-encoding = { version = "0.1", optional = true }
+fastrand = { version = "2.0", optional = true }
+quoted_printable = { version = "0.5", optional = true }
+base64 = { version = "0.22", optional = true }
+email-encoding = { version = "0.2", optional = true }
 
 # file transport
 uuid = { version = "1", features = ["v4"], optional = true }
 serde = { version = "1", optional = true, features = ["derive"] }
 serde_json = { version = "1", optional = true }
 
-# smtp
+# smtp-transport
 nom = { version = "7", optional = true }
 hostname = { version = "0.3", optional = true } # feature
+socket2 = { version = "0.5.1", optional = true }
+url = { version = "2.4", optional = true }
+percent-encoding = { version = "2.3", optional = true }
 
 ## tls
-native-tls = { version = "0.2", optional = true } # feature
-rustls = { version = "0.20", features = ["dangerous_configuration"], optional = true }
-rustls-pemfile = { version = "1", optional = true }
-webpki-roots = { version = "0.22", optional = true }
+native-tls = { version = "0.2.5", optional = true } # feature
+rustls = { version = "0.22.1", optional = true }
+rustls-pemfile = { version = "2", optional = true }
+rustls-native-certs = { version = "0.7", optional = true }
+webpki-roots = { version = "0.26", optional = true }
+boring = { version = "4", optional = true }
 
 # async
 futures-io = { version = "0.3.7", optional = true }
@@ -53,63 +57,80 @@ futures-util = { version = "0.3.7", default-features = false, features = ["io"],
 async-trait = { version = "0.1", optional = true }
 
 ## async-std
-async-std = { version = "1.8", optional = true, features = ["unstable"] }
+async-std = { version = "1.8", optional = true }
 #async-native-tls = { version = "0.3.3", optional = true }
-futures-rustls = { version = "0.22", optional = true }
+futures-rustls = { version = "0.25", optional = true }
 
 ## tokio
-tokio1_crate = { package = "tokio", version = "1", features = ["fs", "rt", "process", "time", "net", "io-util"], optional = true }
+tokio1_crate = { package = "tokio", version = "1", optional = true }
 tokio1_native_tls_crate = { package = "tokio-native-tls", version = "0.3", optional = true }
-tokio1_rustls = { package = "tokio-rustls", version = "0.23", optional = true }
+tokio1_rustls = { package = "tokio-rustls", version = "0.25", optional = true }
+tokio1_boring = { package = "tokio-boring", version = "4", optional = true }
 
 ## dkim
-sha2 = { version = "0.10", optional = true }
-rsa = { version = "0.6.0", optional = true }
-ed25519-dalek = { version = "1.0.1", optional = true }
+sha2 = { version = "0.10", optional = true, features = ["oid"] }
+rsa = { version = "0.9", optional = true }
+ed25519-dalek = { version = "2", optional = true }
+
+# email formats
+email_address = { version = "0.2.1", default-features = false }
 
 [dev-dependencies]
-criterion = "0.3"
+pretty_assertions = "1"
+criterion = "0.5"
+tracing = { version = "0.1.16", default-features = false, features = ["std"] }
 tracing-subscriber = "0.3"
 glob = "0.3"
 walkdir = "2"
 tokio1_crate = { package = "tokio", version = "1", features = ["macros", "rt-multi-thread"] }
 async-std = { version = "1.8", features = ["attributes"] }
 serde_json = "1"
-maud = "0.23"
+maud = "0.26"
 
 [[bench]]
 harness = false
 name = "transport_smtp"
 
+[[bench]]
+harness = false
+name = "mailbox_parsing"
+
 [features]
 default = ["smtp-transport", "pool", "native-tls", "hostname", "builder"]
-builder = ["httpdate", "mime", "base64", "fastrand", "quoted_printable", "email-encoding"]
-mime03 = ["mime"]
+builder = ["dep:httpdate", "dep:mime", "dep:fastrand", "dep:quoted_printable", "dep:email-encoding"]
+mime03 = ["dep:mime"]
 
 # transports
-file-transport = ["uuid"]
-file-transport-envelope = ["serde", "serde_json", "file-transport"]
-sendmail-transport = []
-smtp-transport = ["base64", "nom"]
+file-transport = ["dep:uuid", "tokio1_crate?/fs", "tokio1_crate?/io-util"]
+file-transport-envelope = ["serde", "dep:serde_json", "file-transport"]
+sendmail-transport = ["tokio1_crate?/process", "tokio1_crate?/io-util", "async-std?/unstable"]
+smtp-transport = ["dep:base64", "dep:nom", "dep:socket2", "dep:url", "dep:percent-encoding", "tokio1_crate?/rt", "tokio1_crate?/time", "tokio1_crate?/net"]
 
-pool = ["futures-util"]
+pool = ["dep:futures-util"]
 
-rustls-tls = ["webpki-roots", "rustls", "rustls-pemfile"]
+rustls-tls = ["dep:webpki-roots", "dep:rustls", "dep:rustls-pemfile"]
+
+boring-tls = ["dep:boring"]
 
 # async
-async-std1 = ["async-std", "async-trait", "futures-io", "futures-util"]
-#async-std1-native-tls = ["async-std1", "native-tls", "async-native-tls"]
-async-std1-rustls-tls = ["async-std1", "rustls-tls", "futures-rustls"]
-tokio1 = ["tokio1_crate", "async-trait", "futures-io", "futures-util"]
-tokio1-native-tls = ["tokio1", "native-tls", "tokio1_native_tls_crate"]
-tokio1-rustls-tls = ["tokio1", "rustls-tls", "tokio1_rustls"]
+async-std1 = ["dep:async-std", "dep:async-trait", "dep:futures-io", "dep:futures-util"]
+#async-std1-native-tls = ["async-std1", "native-tls", "dep:async-native-tls"]
+async-std1-rustls-tls = ["async-std1", "rustls-tls", "dep:futures-rustls"]
+tokio1 = ["dep:tokio1_crate", "dep:async-trait", "dep:futures-io", "dep:futures-util"]
+tokio1-native-tls = ["tokio1", "native-tls", "dep:tokio1_native_tls_crate"]
+tokio1-rustls-tls = ["tokio1", "rustls-tls", "dep:tokio1_rustls"]
+tokio1-boring-tls = ["tokio1", "boring-tls", "dep:tokio1_boring"]
 
-dkim = ["sha2", "rsa", "ed25519-dalek"]
+dkim = ["dep:base64", "dep:sha2", "dep:rsa", "dep:ed25519-dalek"]
 
 [package.metadata.docs.rs]
 all-features = true
 rustdoc-args = ["--cfg", "docsrs", "--cfg", "lettre_ignore_tls_mismatch"]
 
+[[example]]
+name = "autoconfigure"
+required-features = ["smtp-transport", "native-tls"]
+
 [[example]]
 name = "basic_html"
 required-features = ["file-transport", "builder"]

README.md

@@ -28,27 +28,14 @@
 </div>
 
 <div align="center">
-  <a href="https://deps.rs/crate/lettre/0.10.0-rc.6">
-    <img src="https://deps.rs/crate/lettre/0.10.0-rc.6/status.svg"
+  <a href="https://deps.rs/crate/lettre/0.11.4">
+    <img src="https://deps.rs/crate/lettre/0.11.4/status.svg"
       alt="dependency status" />
   </a>
 </div>
 
 ---
 
-**NOTE**: this readme refers to the 0.10 version of lettre, which is
-in release candidate state. Use the [`v0.9.x`](https://github.com/lettre/lettre/tree/v0.9.x)
-branch for the previous stable release.
-
-0.10 is already widely used and is already thought to be more reliable than 0.9, so it should generally be used
-for new projects.
-
-We'd love to hear your feedback about 0.10 design and APIs before final release!
-Start a [discussion](https://github.com/lettre/lettre/discussions) in the repository, whether for
-feedback or if you need help or advice using or upgrading lettre 0.10.
-
----
-
 ## Features
 
 Lettre provides the following features:
@@ -63,18 +50,24 @@ Lettre does not provide (for now):
 
 * Email parsing
 
+## Supported Rust Versions
+
+Lettre supports all Rust versions released in the last 6 months. At the time of writing
+the minimum supported Rust version is 1.70, but this could change at any time either from
+one of our dependencies bumping their MSRV or by a new patch release of lettre.
+
 ## Example
 
-This library requires Rust 1.56.0 or newer.
+This library requires Rust 1.70 or newer.
 To use this library, add the following to your `Cargo.toml`:
 
-
 ```toml
 [dependencies]
-lettre = "0.10.0-rc.6"
+lettre = "0.11"
 ```
 
 ```rust,no_run
+use lettre::message::header::ContentType;
 use lettre::transport::smtp::authentication::Credentials;
 use lettre::{Message, SmtpTransport, Transport};
 
@@ -83,10 +76,11 @@ let email = Message::builder()
     .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
     .to("Hei <hei@domain.tld>".parse().unwrap())
     .subject("Happy new year")
+    .header(ContentType::TEXT_PLAIN)
     .body(String::from("Be happy!"))
     .unwrap();
 
-let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
 // Open a remote connection to gmail
 let mailer = SmtpTransport::relay("smtp.gmail.com")
@@ -97,14 +91,22 @@ let mailer = SmtpTransport::relay("smtp.gmail.com")
 // Send the email
 match mailer.send(&email) {
     Ok(_) => println!("Email sent successfully!"),
-    Err(e) => panic!("Could not send email: {:?}", e),
+    Err(e) => panic!("Could not send email: {e:?}"),
 }
 ```
 
+## Not sure of which connect options to use?
+
+Clone the lettre git repository and run the following command (replacing `SMTP_HOST` with your SMTP server's hostname)
+
+```shell
+cargo run --example autoconfigure SMTP_HOST
+```
+
 ## Testing
 
 The `lettre` tests require an open mail server listening locally on port 2525 and the `sendmail` command. If you have python installed 
-such a server can be launched with `python -m smtpd -n -c DebuggingServer localhost:2525`
+such a server can be launched with `python -m smtpd -n -c DebuggingServer 127.0.0.1:2525`
 
 Alternatively only unit tests can be run by doing `cargo test --lib`.
 

SECURITY.md

@@ -2,7 +2,7 @@
 
 The lettre project team welcomes security reports and is committed to providing prompt attention to security issues.
 Security issues should be reported privately via [security@lettre.rs](mailto:security@lettre.rs). Security issues
-should not be reported via the public Github Issue tracker.
+should not be reported via the public GitHub Issue tracker.
 
 ## Security advisories
 

benches/mailbox_parsing.rs

@@ -0,0 +1,27 @@
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use lettre::message::{Mailbox, Mailboxes};
+
+fn bench_parse_single(mailbox: &str) {
+    assert!(mailbox.parse::<Mailbox>().is_ok());
+}
+
+fn bench_parse_multiple(mailboxes: &str) {
+    assert!(mailboxes.parse::<Mailboxes>().is_ok());
+}
+
+fn criterion_benchmark(c: &mut Criterion) {
+    c.bench_function("parse single mailbox", |b| {
+        b.iter(|| bench_parse_single(black_box("\"Benchmark test\" <test@mail.local>")))
+    });
+
+    c.bench_function("parse multiple mailboxes", |b| {
+        b.iter(|| {
+            bench_parse_multiple(black_box(
+                "\"Benchmark test\" <test@mail.local>, Test <test@mail.local>, <test@mail.local>, test@mail.local",
+            ))
+        })
+    });
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);

examples/asyncstd1_smtp_starttls.rs

@@ -1,6 +1,6 @@
 use lettre::{
-    transport::smtp::authentication::Credentials, AsyncSmtpTransport, AsyncStd1Executor,
-    AsyncTransport, Message,
+    message::header::ContentType, transport::smtp::authentication::Credentials, AsyncSmtpTransport,
+    AsyncStd1Executor, AsyncTransport, Message,
 };
 
 #[async_std::main]
@@ -12,10 +12,11 @@ async fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new async year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy with async!"))
         .unwrap();
 
-    let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+    let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
     // Open a remote connection to gmail using STARTTLS
     let mailer: AsyncSmtpTransport<AsyncStd1Executor> =
@@ -27,6 +28,6 @@ async fn main() {
     // Send the email
     match mailer.send(email).await {
         Ok(_) => println!("Email sent successfully!"),
-        Err(e) => panic!("Could not send email: {:?}", e),
+        Err(e) => panic!("Could not send email: {e:?}"),
     }
 }

examples/asyncstd1_smtp_tls.rs

@@ -1,6 +1,6 @@
 use lettre::{
-    transport::smtp::authentication::Credentials, AsyncSmtpTransport, AsyncStd1Executor,
-    AsyncTransport, Message,
+    message::header::ContentType, transport::smtp::authentication::Credentials, AsyncSmtpTransport,
+    AsyncStd1Executor, AsyncTransport, Message,
 };
 
 #[async_std::main]
@@ -12,10 +12,11 @@ async fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new async year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy with async!"))
         .unwrap();
 
-    let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+    let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
     // Open a remote connection to gmail
     let mailer: AsyncSmtpTransport<AsyncStd1Executor> =
@@ -27,6 +28,6 @@ async fn main() {
     // Send the email
     match mailer.send(email).await {
         Ok(_) => println!("Email sent successfully!"),
-        Err(e) => panic!("Could not send email: {:?}", e),
+        Err(e) => panic!("Could not send email: {e:?}"),
     }
 }

examples/autoconfigure.rs

@@ -0,0 +1,93 @@
+use std::{env, process, time::Duration};
+
+use lettre::SmtpTransport;
+
+fn main() {
+    tracing_subscriber::fmt::init();
+
+    let smtp_host = match env::args().nth(1) {
+        Some(smtp_host) => smtp_host,
+        None => {
+            println!("Please provide the SMTP host as the first argument to this command");
+            process::exit(1);
+        }
+    };
+
+    // TLS wrapped connection
+    {
+        tracing::info!(
+            "Trying to establish a TLS wrapped connection to {}",
+            smtp_host
+        );
+
+        let transport = SmtpTransport::relay(&smtp_host)
+            .expect("build SmtpTransport::relay")
+            .timeout(Some(Duration::from_secs(10)))
+            .build();
+        match transport.test_connection() {
+            Ok(true) => {
+                tracing::info!("Successfully connected to {} via a TLS wrapped connection (SmtpTransport::relay). This is the fastest option available for connecting to an SMTP server", smtp_host);
+            }
+            Ok(false) => {
+                tracing::error!("Couldn't connect to {} via a TLS wrapped connection. No more information is available", smtp_host);
+            }
+            Err(err) => {
+                tracing::error!(err = %err, "Couldn't connect to {} via a TLS wrapped connection", smtp_host);
+            }
+        }
+    }
+
+    println!();
+
+    // Plaintext connection which MUST then successfully upgrade to TLS via STARTTLS
+    {
+        tracing::info!("Trying to establish a plaintext connection to {} and then updating it via the SMTP STARTTLS extension", smtp_host);
+
+        let transport = SmtpTransport::starttls_relay(&smtp_host)
+            .expect("build SmtpTransport::starttls_relay")
+            .timeout(Some(Duration::from_secs(10)))
+            .build();
+        match transport.test_connection() {
+            Ok(true) => {
+                tracing::info!("Successfully connected to {} via a plaintext connection which then got upgraded to TLS via the SMTP STARTTLS extension (SmtpTransport::starttls_relay). This is the second best option after the previous TLS wrapped option", smtp_host);
+            }
+            Ok(false) => {
+                tracing::error!(
+                    "Couldn't connect to {} via STARTTLS. No more information is available",
+                    smtp_host
+                );
+            }
+            Err(err) => {
+                tracing::error!(err = %err, "Couldn't connect to {} via STARTTLS", smtp_host);
+            }
+        }
+    }
+
+    println!();
+
+    // Plaintext connection (very insecure)
+    {
+        tracing::info!(
+            "Trying to establish a plaintext connection to {}",
+            smtp_host
+        );
+
+        let transport = SmtpTransport::builder_dangerous(&smtp_host)
+            .timeout(Some(Duration::from_secs(10)))
+            .build();
+        match transport.test_connection() {
+            Ok(true) => {
+                tracing::info!("Successfully connected to {} via a plaintext connection. This option is very insecure and shouldn't be used on the public internet (SmtpTransport::builder_dangerous)", smtp_host);
+            }
+            Ok(false) => {
+                tracing::error!(
+                    "Couldn't connect to {} via a plaintext connection. No more information is available",
+                    smtp_host
+                );
+            }
+            Err(err) => {
+                tracing::error!(err = %err, "Couldn't connect to {} via a plaintext connection", smtp_host);
+            }
+        }
+    }
+}

examples/smtp.rs

@@ -1,4 +1,4 @@
-use lettre::{Message, SmtpTransport, Transport};
+use lettre::{message::header::ContentType, Message, SmtpTransport, Transport};
 
 fn main() {
     tracing_subscriber::fmt::init();
@@ -8,6 +8,7 @@ fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy!"))
         .unwrap();
 
@@ -17,6 +18,6 @@ fn main() {
     // Send the email
     match mailer.send(&email) {
         Ok(_) => println!("Email sent successfully!"),
-        Err(e) => panic!("Could not send email: {:?}", e),
+        Err(e) => panic!("Could not send email: {e:?}"),
     }
 }

examples/smtp_selfsigned.rs

@@ -1,6 +1,7 @@
 use std::fs;
 
 use lettre::{
+    message::header::ContentType,
     transport::smtp::{
         authentication::Credentials,
         client::{Certificate, Tls, TlsParameters},
@@ -16,18 +17,19 @@ fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy!"))
         .unwrap();
 
     // Use a custom certificate stored on disk to securely verify the server's certificate
     let pem_cert = fs::read("certificate.pem").unwrap();
     let cert = Certificate::from_pem(&pem_cert).unwrap();
-    let tls = TlsParameters::builder("smtp.server.com".to_string())
+    let tls = TlsParameters::builder("smtp.server.com".to_owned())
         .add_root_certificate(cert)
         .build()
         .unwrap();
 
-    let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+    let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
     // Open a remote connection to the smtp server
     let mailer = SmtpTransport::builder_dangerous("smtp.server.com")
@@ -39,6 +41,6 @@ fn main() {
     // Send the email
     match mailer.send(&email) {
         Ok(_) => println!("Email sent successfully!"),
-        Err(e) => panic!("Could not send email: {:?}", e),
+        Err(e) => panic!("Could not send email: {e:?}"),
     }
 }

examples/smtp_starttls.rs

@@ -1,4 +1,7 @@
-use lettre::{transport::smtp::authentication::Credentials, Message, SmtpTransport, Transport};
+use lettre::{
+    message::header::ContentType, transport::smtp::authentication::Credentials, Message,
+    SmtpTransport, Transport,
+};
 
 fn main() {
     tracing_subscriber::fmt::init();
@@ -8,10 +11,11 @@ fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy!"))
         .unwrap();
 
-    let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+    let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
     // Open a remote connection to gmail using STARTTLS
     let mailer = SmtpTransport::starttls_relay("smtp.gmail.com")
@@ -22,6 +26,6 @@ fn main() {
     // Send the email
     match mailer.send(&email) {
         Ok(_) => println!("Email sent successfully!"),
-        Err(e) => panic!("Could not send email: {:?}", e),
+        Err(e) => panic!("Could not send email: {e:?}"),
     }
 }

examples/smtp_tls.rs

@@ -1,4 +1,7 @@
-use lettre::{transport::smtp::authentication::Credentials, Message, SmtpTransport, Transport};
+use lettre::{
+    message::header::ContentType, transport::smtp::authentication::Credentials, Message,
+    SmtpTransport, Transport,
+};
 
 fn main() {
     tracing_subscriber::fmt::init();
@@ -8,10 +11,11 @@ fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy!"))
         .unwrap();
 
-    let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+    let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
     // Open a remote connection to gmail
     let mailer = SmtpTransport::relay("smtp.gmail.com")
@@ -22,6 +26,6 @@ fn main() {
     // Send the email
     match mailer.send(&email) {
         Ok(_) => println!("Email sent successfully!"),
-        Err(e) => panic!("Could not send email: {:?}", e),
+        Err(e) => panic!("Could not send email: {e:?}"),
     }
 }

examples/tokio1_smtp_starttls.rs

@@ -2,8 +2,8 @@
 // since it uses Rust 2018 crate renaming to import tokio.
 // Won't be needed in user's code.
 use lettre::{
-    transport::smtp::authentication::Credentials, AsyncSmtpTransport, AsyncTransport, Message,
-    Tokio1Executor,
+    message::header::ContentType, transport::smtp::authentication::Credentials, AsyncSmtpTransport,
+    AsyncTransport, Message, Tokio1Executor,
 };
 use tokio1_crate as tokio;
 
@@ -16,10 +16,11 @@ async fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new async year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy with async!"))
         .unwrap();
 
-    let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+    let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
     // Open a remote connection to gmail using STARTTLS
     let mailer: AsyncSmtpTransport<Tokio1Executor> =
@@ -31,6 +32,6 @@ async fn main() {
     // Send the email
     match mailer.send(email).await {
         Ok(_) => println!("Email sent successfully!"),
-        Err(e) => panic!("Could not send email: {:?}", e),
+        Err(e) => panic!("Could not send email: {e:?}"),
     }
 }

examples/tokio1_smtp_tls.rs

@@ -2,8 +2,8 @@
 // since it uses Rust 2018 crate renaming to import tokio.
 // Won't be needed in user's code.
 use lettre::{
-    transport::smtp::authentication::Credentials, AsyncSmtpTransport, AsyncTransport, Message,
-    Tokio1Executor,
+    message::header::ContentType, transport::smtp::authentication::Credentials, AsyncSmtpTransport,
+    AsyncTransport, Message, Tokio1Executor,
 };
 use tokio1_crate as tokio;
 
@@ -16,10 +16,11 @@ async fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new async year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy with async!"))
         .unwrap();
 
-    let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+    let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
     // Open a remote connection to gmail
     let mailer: AsyncSmtpTransport<Tokio1Executor> =
@@ -31,6 +32,6 @@ async fn main() {
     // Send the email
     match mailer.send(email).await {
         Ok(_) => println!("Email sent successfully!"),
-        Err(e) => panic!("Could not send email: {:?}", e),
+        Err(e) => panic!("Could not send email: {e:?}"),
     }
 }

src/address/types.rs

@@ -8,15 +8,14 @@ use std::{
     str::FromStr,
 };
 
+use email_address::EmailAddress;
 use idna::domain_to_ascii;
-use once_cell::sync::Lazy;
-use regex::Regex;
 
 /// Represents an email address with a user and a domain name.
 ///
 /// This type contains email in canonical form (_user@domain.tld_).
 ///
-/// **NOTE**: Enable feature "serde" to be able serialize/deserialize it using [serde](https://serde.rs/).
+/// **NOTE**: Enable feature "serde" to be able to serialize/deserialize it using [serde](https://serde.rs/).
 ///
 /// # Examples
 ///
@@ -55,20 +54,6 @@ pub struct Address {
     at_start: usize,
 }
 
-// Regex from the specs
-// https://html.spec.whatwg.org/multipage/forms.html#valid-e-mail-address
-// It will mark esoteric email addresses like quoted string as invalid
-static USER_RE: Lazy<Regex> =
-    Lazy::new(|| Regex::new(r"^(?i)[a-z0-9.!#$%&'*+/=?^_`{|}~-]+\z").unwrap());
-static DOMAIN_RE: Lazy<Regex> = Lazy::new(|| {
-    Regex::new(
-        r"(?i)^[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?(?:.[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?)*$",
-    )
-    .unwrap()
-});
-// literal form, ipv4 or ipv6 address (SMTP 4.1.3)
-static LITERAL_RE: Lazy<Regex> = Lazy::new(|| Regex::new(r"(?i)\[([A-f0-9:\.]+)\]\z").unwrap());
-
 impl Address {
     /// Creates a new email address from a user and domain.
     ///
@@ -126,7 +111,7 @@ impl Address {
     }
 
     pub(super) fn check_user(user: &str) -> Result<(), AddressError> {
-        if USER_RE.is_match(user) {
+        if EmailAddress::is_valid_local_part(user) {
             Ok(())
         } else {
             Err(AddressError::InvalidUser)
@@ -142,16 +127,19 @@ impl Address {
     }
 
     fn check_domain_ascii(domain: &str) -> Result<(), AddressError> {
-        if DOMAIN_RE.is_match(domain) {
+        // Domain
+        if EmailAddress::is_valid_domain(domain) {
             return Ok(());
         }
 
-        if let Some(caps) = LITERAL_RE.captures(domain) {
-            if let Some(cap) = caps.get(1) {
-                if cap.as_str().parse::<IpAddr>().is_ok() {
-                    return Ok(());
-                }
-            }
+        // IP
+        let ip = domain
+            .strip_prefix('[')
+            .and_then(|ip| ip.strip_suffix(']'))
+            .unwrap_or(domain);
+
+        if ip.parse::<IpAddr>().is_ok() {
+            return Ok(());
         }
 
         Err(AddressError::InvalidDomain)
@@ -196,7 +184,7 @@ where
         let domain = domain.as_ref();
         Address::check_domain(domain)?;
 
-        let serialized = format!("{}@{}", user, domain);
+        let serialized = format!("{user}@{domain}");
         Ok(Address {
             serialized,
             at_start: user.len(),
@@ -238,7 +226,8 @@ fn check_address(val: &str) -> Result<usize, AddressError> {
     Ok(user.len())
 }
 
-#[derive(Debug, PartialEq, Clone, Copy)]
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+#[non_exhaustive]
 /// Errors in email addresses parsing
 pub enum AddressError {
     /// Missing domain or user
@@ -249,6 +238,8 @@ pub enum AddressError {
     InvalidUser,
     /// Invalid email domain
     InvalidDomain,
+    /// Invalid input found
+    InvalidInput,
 }
 
 impl Error for AddressError {}
@@ -260,6 +251,7 @@ impl Display for AddressError {
             AddressError::Unbalanced => f.write_str("Unbalanced angle bracket"),
             AddressError::InvalidUser => f.write_str("Invalid email user"),
             AddressError::InvalidDomain => f.write_str("Invalid email domain"),
+            AddressError::InvalidInput => f.write_str("Invalid input"),
         }
     }
 }
@@ -269,7 +261,7 @@ mod tests {
     use super::*;
 
     #[test]
-    fn parse_address() {
+    fn ascii_address() {
         let addr_str = "something@example.com";
         let addr = Address::from_str(addr_str).unwrap();
         let addr2 = Address::new("something", "example.com").unwrap();
@@ -279,4 +271,36 @@ mod tests {
         assert_eq!(addr2.user(), "something");
         assert_eq!(addr2.domain(), "example.com");
     }
+
+    #[test]
+    fn ascii_address_ipv4() {
+        let addr_str = "something@1.1.1.1";
+        let addr = Address::from_str(addr_str).unwrap();
+        let addr2 = Address::new("something", "1.1.1.1").unwrap();
+        assert_eq!(addr, addr2);
+        assert_eq!(addr.user(), "something");
+        assert_eq!(addr.domain(), "1.1.1.1");
+        assert_eq!(addr2.user(), "something");
+        assert_eq!(addr2.domain(), "1.1.1.1");
+    }
+
+    #[test]
+    fn ascii_address_ipv6() {
+        let addr_str = "something@[2606:4700:4700::1111]";
+        let addr = Address::from_str(addr_str).unwrap();
+        let addr2 = Address::new("something", "[2606:4700:4700::1111]").unwrap();
+        assert_eq!(addr, addr2);
+        assert_eq!(addr.user(), "something");
+        assert_eq!(addr.domain(), "[2606:4700:4700::1111]");
+        assert_eq!(addr2.user(), "something");
+        assert_eq!(addr2.domain(), "[2606:4700:4700::1111]");
+    }
+
+    #[test]
+    fn check_parts() {
+        assert!(Address::check_user("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa").is_err());
+        assert!(
+            Address::check_domain("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.com").is_err()
+        );
+    }
 }

src/base64.rs

@@ -0,0 +1,12 @@
+use ::base64::{
+    engine::{general_purpose::STANDARD, Engine},
+    DecodeError,
+};
+
+pub(crate) fn encode<T: AsRef<[u8]>>(input: T) -> String {
+    STANDARD.encode(input)
+}
+
+pub(crate) fn decode<T: AsRef<[u8]>>(input: T) -> Result<Vec<u8>, DecodeError> {
+    STANDARD.decode(input)
+}

src/executor.rs

@@ -109,7 +109,6 @@ impl Executor for Tokio1Executor {
     #[cfg(feature = "smtp-transport")]
     type Sleep = tokio1_crate::time::Sleep;
 
-    #[doc(hidden)]
     #[cfg(feature = "smtp-transport")]
     fn spawn<F>(fut: F) -> Self::Handle
     where
@@ -119,13 +118,11 @@ impl Executor for Tokio1Executor {
         tokio1_crate::spawn(fut)
     }
 
-    #[doc(hidden)]
     #[cfg(feature = "smtp-transport")]
     fn sleep(duration: Duration) -> Self::Sleep {
         tokio1_crate::time::sleep(duration)
     }
 
-    #[doc(hidden)]
     #[cfg(feature = "smtp-transport")]
     async fn connect(
         hostname: &str,
@@ -137,7 +134,7 @@ impl Executor for Tokio1Executor {
         #[allow(clippy::match_single_binding)]
         let tls_parameters = match tls {
             #[cfg(any(feature = "tokio1-native-tls", feature = "tokio1-rustls-tls"))]
-            Tls::Wrapper(ref tls_parameters) => Some(tls_parameters.clone()),
+            Tls::Wrapper(tls_parameters) => Some(tls_parameters.clone()),
             _ => None,
         };
         #[allow(unused_mut)]
@@ -146,18 +143,19 @@ impl Executor for Tokio1Executor {
             timeout,
             hello_name,
             tls_parameters,
+            None,
         )
         .await?;
 
         #[cfg(any(feature = "tokio1-native-tls", feature = "tokio1-rustls-tls"))]
         match tls {
-            Tls::Opportunistic(ref tls_parameters) => {
+            Tls::Opportunistic(tls_parameters) => {
                 if conn.can_starttls() {
-                    conn.starttls(tls_parameters.clone(), hello_name).await?;
+                    conn = conn.starttls(tls_parameters.clone(), hello_name).await?;
                 }
             }
-            Tls::Required(ref tls_parameters) => {
-                conn.starttls(tls_parameters.clone(), hello_name).await?;
+            Tls::Required(tls_parameters) => {
+                conn = conn.starttls(tls_parameters.clone(), hello_name).await?;
             }
             _ => (),
         }
@@ -165,13 +163,11 @@ impl Executor for Tokio1Executor {
         Ok(conn)
     }
 
-    #[doc(hidden)]
     #[cfg(feature = "file-transport-envelope")]
     async fn fs_read(path: &Path) -> IoResult<Vec<u8>> {
         tokio1_crate::fs::read(path).await
     }
 
-    #[doc(hidden)]
     #[cfg(feature = "file-transport")]
     async fn fs_write(path: &Path, contents: &[u8]) -> IoResult<()> {
         tokio1_crate::fs::write(path, contents).await
@@ -209,7 +205,6 @@ impl Executor for AsyncStd1Executor {
     #[cfg(feature = "smtp-transport")]
     type Sleep = BoxFuture<'static, ()>;
 
-    #[doc(hidden)]
     #[cfg(feature = "smtp-transport")]
     fn spawn<F>(fut: F) -> Self::Handle
     where
@@ -219,14 +214,12 @@ impl Executor for AsyncStd1Executor {
         async_std::task::spawn(fut)
     }
 
-    #[doc(hidden)]
     #[cfg(feature = "smtp-transport")]
     fn sleep(duration: Duration) -> Self::Sleep {
-        let fut = async move { async_std::task::sleep(duration).await };
+        let fut = async_std::task::sleep(duration);
         Box::pin(fut)
     }
 
-    #[doc(hidden)]
     #[cfg(feature = "smtp-transport")]
     async fn connect(
         hostname: &str,
@@ -238,7 +231,7 @@ impl Executor for AsyncStd1Executor {
         #[allow(clippy::match_single_binding)]
         let tls_parameters = match tls {
             #[cfg(any(feature = "async-std1-native-tls", feature = "async-std1-rustls-tls"))]
-            Tls::Wrapper(ref tls_parameters) => Some(tls_parameters.clone()),
+            Tls::Wrapper(tls_parameters) => Some(tls_parameters.clone()),
             _ => None,
         };
         #[allow(unused_mut)]
@@ -252,13 +245,13 @@ impl Executor for AsyncStd1Executor {
 
         #[cfg(any(feature = "async-std1-native-tls", feature = "async-std1-rustls-tls"))]
         match tls {
-            Tls::Opportunistic(ref tls_parameters) => {
+            Tls::Opportunistic(tls_parameters) => {
                 if conn.can_starttls() {
-                    conn.starttls(tls_parameters.clone(), hello_name).await?;
+                    conn = conn.starttls(tls_parameters.clone(), hello_name).await?;
                 }
             }
-            Tls::Required(ref tls_parameters) => {
-                conn.starttls(tls_parameters.clone(), hello_name).await?;
+            Tls::Required(tls_parameters) => {
+                conn = conn.starttls(tls_parameters.clone(), hello_name).await?;
             }
             _ => (),
         }
@@ -266,13 +259,11 @@ impl Executor for AsyncStd1Executor {
         Ok(conn)
     }
 
-    #[doc(hidden)]
     #[cfg(feature = "file-transport-envelope")]
     async fn fs_read(path: &Path) -> IoResult<Vec<u8>> {
         async_std::fs::read(path).await
     }
 
-    #[doc(hidden)]
     #[cfg(feature = "file-transport")]
     async fn fs_write(path: &Path, contents: &[u8]) -> IoResult<()> {
         async_std::fs::write(path, contents).await
@@ -288,15 +279,13 @@ impl SpawnHandle for async_std::task::JoinHandle<()> {
 }
 
 mod private {
-    use super::*;
-
     pub trait Sealed {}
 
     #[cfg(feature = "tokio1")]
-    impl Sealed for Tokio1Executor {}
+    impl Sealed for super::Tokio1Executor {}
 
     #[cfg(feature = "async-std1")]
-    impl Sealed for AsyncStd1Executor {}
+    impl Sealed for super::AsyncStd1Executor {}
 
     #[cfg(all(feature = "smtp-transport", feature = "tokio1"))]
     impl Sealed for tokio1_crate::task::JoinHandle<()> {}

src/lib.rs

@@ -6,7 +6,7 @@
 //! * Secure defaults
 //! * Async support
 //!
-//! Lettre requires Rust 1.56.0 or newer.
+//! Lettre requires Rust 1.70 or newer.
 //!
 //! ## Features
 //!
@@ -41,6 +41,15 @@
 //!
 //! NOTE: native-tls isn't supported with `async-std`
 //!
+//! #### SMTP over TLS via the boring crate (Boring TLS)
+//!
+//! _Secure SMTP connections using TLS from the `boring-tls` crate_
+//!
+//! * **boring-tls**: TLS support for the synchronous version of the API
+//! * **tokio1-boring-tls**: TLS support for the `tokio1` async version of the API
+//!
+//! NOTE: boring-tls isn't supported with `async-std`
+//!
 //! #### SMTP over TLS via the rustls crate
 //!
 //! _Secure SMTP connections using TLS from the `rustls-tls` crate_
@@ -100,7 +109,7 @@
 //! [mime 0.3]: https://docs.rs/mime/0.3
 //! [DKIM]: https://datatracker.ietf.org/doc/html/rfc6376
 
-#![doc(html_root_url = "https://docs.rs/crate/lettre/0.10.0-rc.6")]
+#![doc(html_root_url = "https://docs.rs/crate/lettre/0.11.4")]
 #![doc(html_favicon_url = "https://lettre.rs/favicon.ico")]
 #![doc(html_logo_url = "https://avatars0.githubusercontent.com/u/15113230?v=4")]
 #![forbid(unsafe_code)]
@@ -112,12 +121,32 @@
     unused_import_braces,
     rust_2018_idioms,
     clippy::string_add,
-    clippy::string_add_assign
+    clippy::string_add_assign,
+    clippy::clone_on_ref_ptr,
+    clippy::verbose_file_reads,
+    clippy::unnecessary_self_imports,
+    clippy::string_to_string,
+    clippy::mem_forget,
+    clippy::cast_lossless,
+    clippy::inefficient_to_string,
+    clippy::inline_always,
+    clippy::linkedlist,
+    clippy::macro_use_imports,
+    clippy::manual_assert,
+    clippy::unnecessary_join,
+    clippy::wildcard_imports,
+    clippy::str_to_string,
+    clippy::empty_structs_with_brackets,
+    clippy::zero_sized_map_values
 )]
 #![cfg_attr(docsrs, feature(doc_cfg))]
 
 #[cfg(not(lettre_ignore_tls_mismatch))]
 mod compiletime_checks {
+    #[cfg(all(feature = "native-tls", feature = "boring-tls"))]
+    compile_error!("feature \"native-tls\" and feature \"boring-tls\" cannot be enabled at the same time, otherwise
+    the executable will fail to link.");
+
     #[cfg(all(
         feature = "tokio1",
         feature = "native-tls",
@@ -136,6 +165,15 @@ mod compiletime_checks {
     If you'd like to use `native-tls` make sure that the `rustls-tls` feature hasn't been enabled by mistake.
     Make sure to apply the same to any of your crate dependencies that use the `lettre` crate.");
 
+    #[cfg(all(
+        feature = "tokio1",
+        feature = "boring-tls",
+        not(feature = "tokio1-boring-tls")
+    ))]
+    compile_error!("Lettre is being built with the `tokio1` and the `boring-tls` features, but the `tokio1-boring-tls` feature hasn't been turned on.
+    If you'd like to use `boring-tls` make sure that the `rustls-tls` feature hasn't been enabled by mistake.
+    Make sure to apply the same to any of your crate dependencies that use the `lettre` crate.");
+
     /*
     #[cfg(all(
         feature = "async-std1",
@@ -167,6 +205,8 @@ Make sure to apply the same to any of your crate dependencies that use the `lett
 }
 
 pub mod address;
+#[cfg(any(feature = "smtp-transport", feature = "dkim"))]
+mod base64;
 pub mod error;
 #[cfg(any(feature = "tokio1", feature = "async-std1"))]
 mod executor;
@@ -179,11 +219,11 @@ use std::error::Error as StdError;
 
 #[cfg(feature = "async-std1")]
 pub use self::executor::AsyncStd1Executor;
-#[cfg(all(any(feature = "tokio1", feature = "async-std1")))]
+#[cfg(any(feature = "tokio1", feature = "async-std1"))]
 pub use self::executor::Executor;
 #[cfg(feature = "tokio1")]
 pub use self::executor::Tokio1Executor;
-#[cfg(all(any(feature = "tokio1", feature = "async-std1")))]
+#[cfg(any(feature = "tokio1", feature = "async-std1"))]
 #[doc(inline)]
 pub use self::transport::AsyncTransport;
 pub use crate::address::Address;

src/message/attachment.rs

@@ -13,9 +13,9 @@ pub struct Attachment {
 
 #[derive(Clone)]
 enum Disposition {
-    /// file name
+    /// File name
     Attached(String),
-    /// content id
+    /// Content id
     Inline(String),
 }
 
@@ -96,7 +96,7 @@ impl Attachment {
                 builder.header(header::ContentDisposition::attachment(&filename))
             }
             Disposition::Inline(content_id) => builder
-                .header(header::ContentId::from(format!("<{}>", content_id)))
+                .header(header::ContentId::from(format!("<{content_id}>")))
                 .header(header::ContentDisposition::inline()),
         };
         builder = builder.header(content_type);

src/message/body.rs

@@ -1,8 +1,4 @@
-use std::{
-    io::{self, Write},
-    mem,
-    ops::Deref,
-};
+use std::{mem, ops::Deref};
 
 use crate::message::header::ContentTransferEncoding;
 
@@ -41,7 +37,7 @@ impl Body {
     pub fn new<B: Into<MaybeString>>(buf: B) -> Self {
         let mut buf: MaybeString = buf.into();
 
-        let encoding = buf.encoding();
+        let encoding = buf.encoding(false);
         buf.encode_crlf();
         Self::new_impl(buf.into(), encoding)
     }
@@ -61,7 +57,22 @@ impl Body {
     ) -> Result<Self, Vec<u8>> {
         let mut buf: MaybeString = buf.into();
 
-        if !buf.is_encoding_ok(encoding) {
+        let best_encoding = buf.encoding(true);
+        let ok = match (encoding, best_encoding) {
+            (ContentTransferEncoding::SevenBit, ContentTransferEncoding::SevenBit) => true,
+            (
+                ContentTransferEncoding::EightBit,
+                ContentTransferEncoding::SevenBit | ContentTransferEncoding::EightBit,
+            ) => true,
+            (ContentTransferEncoding::SevenBit | ContentTransferEncoding::EightBit, _) => false,
+            (
+                ContentTransferEncoding::QuotedPrintable
+                | ContentTransferEncoding::Base64
+                | ContentTransferEncoding::Binary,
+                _,
+            ) => true,
+        };
+        if !ok {
             return Err(buf.into());
         }
 
@@ -91,36 +102,13 @@ impl Body {
                 Self::dangerous_pre_encoded(encoded, ContentTransferEncoding::QuotedPrintable)
             }
             ContentTransferEncoding::Base64 => {
-                let base64_len = buf.len() * 4 / 3 + 4;
-                let base64_endings_len = base64_len + base64_len / LINE_MAX_LENGTH;
+                let len = email_encoding::body::base64::encoded_len(buf.len());
 
-                let mut out = Vec::with_capacity(base64_endings_len);
-                {
-                    let writer = LineWrappingWriter::new(&mut out, LINE_MAX_LENGTH);
-                    let mut writer = base64::write::EncoderWriter::new(writer, base64::STANDARD);
+                let mut out = String::with_capacity(len);
+                email_encoding::body::base64::encode(&buf, &mut out)
+                    .expect("encode body as base64");
 
-                    // TODO: use writer.write_all(self.as_ref()).expect("base64 encoding never fails");
-
-                    // modified Write::write_all to work around base64 crate bug
-                    // TODO: remove once https://github.com/marshallpierce/rust-base64/issues/148 is fixed
-                    {
-                        let mut buf: &[u8] = buf.as_ref();
-                        while !buf.is_empty() {
-                            match writer.write(buf) {
-                                Ok(0) => {
-                                    // ignore 0 writes
-                                }
-                                Ok(n) => {
-                                    buf = &buf[n..];
-                                }
-                                Err(ref e) if e.kind() == std::io::ErrorKind::Interrupted => {}
-                                Err(e) => panic!("base64 encoding never fails: {}", e),
-                            }
-                        }
-                    }
-                }
-
-                Self::dangerous_pre_encoded(out, ContentTransferEncoding::Base64)
+                Self::dangerous_pre_encoded(out.into_bytes(), ContentTransferEncoding::Base64)
             }
         }
     }
@@ -153,21 +141,20 @@ impl Body {
 impl MaybeString {
     /// Suggests the best `Content-Transfer-Encoding` to be used for this `MaybeString`
     ///
-    /// If the `MaybeString` was created from a `String` composed only of US-ASCII
-    /// characters, with no lines longer than 1000 characters, then 7bit
-    /// encoding will be used, else quoted-printable will be chosen.
-    ///
-    /// If the `MaybeString` was instead created from a `Vec<u8>`, base64 encoding is always
-    /// chosen.
-    ///
-    /// `8bit` and `binary` encodings are never returned, as they may not be
-    /// supported by all SMTP servers.
-    pub fn encoding(&self) -> ContentTransferEncoding {
-        match &self {
-            Self::String(s) if is_7bit_encoded(s.as_ref()) => ContentTransferEncoding::SevenBit,
-            // TODO: consider when base64 would be a better option because of output size
-            Self::String(_) => ContentTransferEncoding::QuotedPrintable,
-            Self::Binary(_) => ContentTransferEncoding::Base64,
+    /// The `binary` encoding is never returned
+    fn encoding(&self, supports_utf8: bool) -> ContentTransferEncoding {
+        use email_encoding::body::Encoding;
+
+        let output = match self {
+            Self::String(s) => Encoding::choose(s.as_str(), supports_utf8),
+            Self::Binary(b) => Encoding::choose(b.as_slice(), supports_utf8),
+        };
+
+        match output {
+            Encoding::SevenBit => ContentTransferEncoding::SevenBit,
+            Encoding::EightBit => ContentTransferEncoding::EightBit,
+            Encoding::QuotedPrintable => ContentTransferEncoding::QuotedPrintable,
+            Encoding::Base64 => ContentTransferEncoding::Base64,
         }
     }
 
@@ -178,18 +165,6 @@ impl MaybeString {
             Self::Binary(_) => {}
         }
     }
-
-    /// Returns `true` if using `encoding` to encode this `MaybeString`
-    /// would result into an invalid encoded body.
-    fn is_encoding_ok(&self, encoding: ContentTransferEncoding) -> bool {
-        match encoding {
-            ContentTransferEncoding::SevenBit => is_7bit_encoded(self),
-            ContentTransferEncoding::EightBit => is_8bit_encoded(self),
-            ContentTransferEncoding::Binary
-            | ContentTransferEncoding::QuotedPrintable
-            | ContentTransferEncoding::Base64 => true,
-        }
-    }
 }
 
 /// A trait for something that takes an encoded [`Body`].
@@ -273,73 +248,6 @@ impl Deref for MaybeString {
     }
 }
 
-/// Checks whether it contains only US-ASCII characters,
-/// and no lines are longer than 1000 characters including the `\n` character.
-///
-/// Most efficient content encoding available
-fn is_7bit_encoded(buf: &[u8]) -> bool {
-    buf.is_ascii() && !contains_too_long_lines(buf)
-}
-
-/// Checks that no lines are longer than 1000 characters,
-/// including the `\n` character.
-/// NOTE: 8bit isn't supported by all SMTP servers.
-fn is_8bit_encoded(buf: &[u8]) -> bool {
-    !contains_too_long_lines(buf)
-}
-
-/// Checks if there are lines that are longer than 1000 characters,
-/// including the `\n` character.
-fn contains_too_long_lines(buf: &[u8]) -> bool {
-    buf.len() > 1000 && buf.split(|&b| b == b'\n').any(|line| line.len() > 999)
-}
-
-const LINE_SEPARATOR: &[u8] = b"\r\n";
-const LINE_MAX_LENGTH: usize = 78 - LINE_SEPARATOR.len();
-
-/// A `Write`r that inserts a line separator `\r\n` every `max_line_length` bytes.
-struct LineWrappingWriter<'a, W> {
-    writer: &'a mut W,
-    current_line_length: usize,
-    max_line_length: usize,
-}
-
-impl<'a, W> LineWrappingWriter<'a, W> {
-    pub fn new(writer: &'a mut W, max_line_length: usize) -> Self {
-        Self {
-            writer,
-            current_line_length: 0,
-            max_line_length,
-        }
-    }
-}
-
-impl<'a, W> Write for LineWrappingWriter<'a, W>
-where
-    W: Write,
-{
-    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
-        let remaining_line_len = self.max_line_length - self.current_line_length;
-        let write_len = std::cmp::min(buf.len(), remaining_line_len);
-
-        self.writer.write_all(&buf[..write_len])?;
-
-        if remaining_line_len == write_len {
-            self.writer.write_all(LINE_SEPARATOR)?;
-
-            self.current_line_length = 0;
-        } else {
-            self.current_line_length += write_len;
-        }
-
-        Ok(write_len)
-    }
-
-    fn flush(&mut self) -> io::Result<()> {
-        self.writer.flush()
-    }
-}
-
 /// In place conversion to CRLF line endings
 fn in_place_crlf_line_endings(string: &mut String) {
     let indices = find_all_lf_char_indices(string);
@@ -377,6 +285,8 @@ fn find_all_lf_char_indices(s: &str) -> Vec<usize> {
 
 #[cfg(test)]
 mod test {
+    use pretty_assertions::assert_eq;
+
     use super::{in_place_crlf_line_endings, Body, ContentTransferEncoding};
 
     #[test]
@@ -509,13 +419,10 @@ mod test {
 
     #[test]
     fn quoted_printable_detect() {
-        let encoded = Body::new(String::from("Привет, мир!"));
+        let encoded = Body::new(String::from("Questo messaggio è corto"));
 
         assert_eq!(encoded.encoding(), ContentTransferEncoding::QuotedPrintable);
-        assert_eq!(
-            encoded.as_ref(),
-            b"=D0=9F=D1=80=D0=B8=D0=B2=D0=B5=D1=82, =D0=BC=D0=B8=D1=80!".as_ref()
-        );
+        assert_eq!(encoded.as_ref(), b"Questo messaggio =C3=A8 corto");
     }
 
     #[test]
@@ -547,14 +454,17 @@ mod test {
 
     #[test]
     fn quoted_printable_encode_line_wrap() {
-        let encoded = Body::new(String::from("Текст письма в уникоде"));
+        let encoded = Body::new(String::from(
+            "Se lo standard 📬 fosse stato più semplice avremmo finito molto prima.",
+        ));
 
         assert_eq!(encoded.encoding(), ContentTransferEncoding::QuotedPrintable);
+        println!("{}", std::str::from_utf8(encoded.as_ref()).unwrap());
         assert_eq!(
             encoded.as_ref(),
             concat!(
-                "=D0=A2=D0=B5=D0=BA=D1=81=D1=82 =D0=BF=D0=B8=D1=81=D1=8C=D0=BC=D0=B0 =D0=B2 =\r\n",
-                "=D1=83=D0=BD=D0=B8=D0=BA=D0=BE=D0=B4=D0=B5"
+                "Se lo standard =F0=9F=93=AC fosse stato pi=C3=B9 semplice avremmo finito mo=\r\n",
+                "lto prima."
             )
             .as_bytes()
         );
@@ -562,27 +472,31 @@ mod test {
 
     #[test]
     fn base64_detect() {
-        let input = Body::new(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
+        let input = Body::new(vec![0; 80]);
         let encoding = input.encoding();
         assert_eq!(encoding, ContentTransferEncoding::Base64);
     }
 
     #[test]
     fn base64_encode_bytes() {
-        let encoded = Body::new_with_encoding(
-            vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
-            ContentTransferEncoding::Base64,
-        )
-        .unwrap();
+        let encoded =
+            Body::new_with_encoding(vec![0; 80], ContentTransferEncoding::Base64).unwrap();
 
         assert_eq!(encoded.encoding(), ContentTransferEncoding::Base64);
-        assert_eq!(encoded.as_ref(), b"AAECAwQFBgcICQ==");
+        assert_eq!(
+            encoded.as_ref(),
+            concat!(
+                "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA\r\n",
+                "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA="
+            )
+            .as_bytes()
+        );
     }
 
     #[test]
     fn base64_encode_bytes_wrapping() {
         let encoded = Body::new_with_encoding(
-            vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9].repeat(20),
+            [0, 1, 2, 3, 4, 5, 6, 7, 8, 9].repeat(20),
             ContentTransferEncoding::Base64,
         )
         .unwrap();

src/message/dkim.rs

@@ -1,15 +1,12 @@
 use std::{
     borrow::Cow,
     error::Error as StdError,
-    fmt::{self, Display, Write},
-    iter::IntoIterator,
+    fmt::{self, Display},
     time::SystemTime,
 };
 
 use ed25519_dalek::Signer;
-use once_cell::sync::Lazy;
-use regex::{bytes::Regex as BRegex, Regex};
-use rsa::{pkcs1::DecodeRsaPrivateKey, Hash, PaddingScheme, RsaPrivateKey};
+use rsa::{pkcs1::DecodeRsaPrivateKey, pkcs1v15::Pkcs1v15Sign, RsaPrivateKey};
 use sha2::{Digest, Sha256};
 
 use crate::message::{
@@ -96,9 +93,9 @@ impl Display for DkimSigningKeyError {
 impl StdError for DkimSigningKeyError {
     fn source(&self) -> Option<&(dyn StdError + 'static)> {
         Some(match &self.0 {
-            InnerDkimSigningKeyError::Base64(err) => &*err,
-            InnerDkimSigningKeyError::Rsa(err) => &*err,
-            InnerDkimSigningKeyError::Ed25519(err) => &*err,
+            InnerDkimSigningKeyError::Base64(err) => err,
+            InnerDkimSigningKeyError::Rsa(err) => err,
+            InnerDkimSigningKeyError::Ed25519(err) => err,
         })
     }
 }
@@ -110,26 +107,30 @@ pub struct DkimSigningKey(InnerDkimSigningKey);
 #[derive(Debug)]
 enum InnerDkimSigningKey {
     Rsa(RsaPrivateKey),
-    Ed25519(ed25519_dalek::Keypair),
+    Ed25519(ed25519_dalek::SigningKey),
 }
 
 impl DkimSigningKey {
     pub fn new(
-        private_key: String,
+        private_key: &str,
         algorithm: DkimSigningAlgorithm,
     ) -> Result<DkimSigningKey, DkimSigningKeyError> {
         Ok(Self(match algorithm {
             DkimSigningAlgorithm::Rsa => InnerDkimSigningKey::Rsa(
-                RsaPrivateKey::from_pkcs1_pem(&private_key)
+                RsaPrivateKey::from_pkcs1_pem(private_key)
                     .map_err(|err| DkimSigningKeyError(InnerDkimSigningKeyError::Rsa(err)))?,
             ),
             DkimSigningAlgorithm::Ed25519 => {
-                InnerDkimSigningKey::Ed25519(
-                    ed25519_dalek::Keypair::from_bytes(&base64::decode(private_key).map_err(
-                        |err| DkimSigningKeyError(InnerDkimSigningKeyError::Base64(err)),
-                    )?)
-                    .map_err(|err| DkimSigningKeyError(InnerDkimSigningKeyError::Ed25519(err)))?,
-                )
+                InnerDkimSigningKey::Ed25519(ed25519_dalek::SigningKey::from_bytes(
+                    &crate::base64::decode(private_key)
+                        .map_err(|err| DkimSigningKeyError(InnerDkimSigningKeyError::Base64(err)))?
+                        .try_into()
+                        .map_err(|_| {
+                            DkimSigningKeyError(InnerDkimSigningKeyError::Ed25519(
+                                ed25519_dalek::ed25519::Error::new(),
+                            ))
+                        })?,
+                ))
             }
         }))
     }
@@ -142,19 +143,18 @@ impl DkimSigningKey {
 }
 
 /// A struct to describe Dkim configuration applied when signing a message
-/// selector: the name of the key publied in DNS
-/// domain: the domain for which we sign the message
-/// private_key: private key in PKCS1 string format
-/// headers: a list of headers name to be included in the signature. Signing of more than one
-/// header with same name is not supported
-/// canonicalization: the canonicalization to be applied on the message
-/// pub signing_algorithm: the signing algorithm to be used when signing
 #[derive(Debug)]
 pub struct DkimConfig {
+    /// The name of the key published in DNS
     selector: String,
+    /// The domain for which we sign the message
     domain: String,
+    /// The private key in PKCS1 string format
     private_key: DkimSigningKey,
+    /// A list of header names to be included in the signature. Signing of more than one
+    /// header with the same name is not supported
     headers: Vec<HeaderName>,
+    /// The signing algorithm to be used when signing
     canonicalization: DkimCanonicalization,
 }
 
@@ -219,45 +219,91 @@ fn dkim_header_format(
 
 /// Canonicalize the body of an email
 fn dkim_canonicalize_body(
-    body: &[u8],
+    mut body: &[u8],
     canonicalization: DkimCanonicalizationType,
 ) -> Cow<'_, [u8]> {
-    static RE: Lazy<BRegex> = Lazy::new(|| BRegex::new("(\r\n)+$").unwrap());
-    static RE_DOUBLE_SPACE: Lazy<BRegex> = Lazy::new(|| BRegex::new("[\\t ]+").unwrap());
-    static RE_SPACE_EOL: Lazy<BRegex> = Lazy::new(|| BRegex::new("[\t ]\r\n").unwrap());
     match canonicalization {
-        DkimCanonicalizationType::Simple => RE.replace(body, &b"\r\n"[..]),
-        DkimCanonicalizationType::Relaxed => {
-            let body = RE_DOUBLE_SPACE.replace_all(body, &b" "[..]);
-            let body = match RE_SPACE_EOL.replace_all(&body, &b"\r\n"[..]) {
-                Cow::Borrowed(_body) => body,
-                Cow::Owned(body) => Cow::Owned(body),
-            };
-            match RE.replace(&body, &b"\r\n"[..]) {
-                Cow::Borrowed(_body) => body,
-                Cow::Owned(body) => Cow::Owned(body),
+        DkimCanonicalizationType::Simple => {
+            // Remove empty lines at end
+            while body.ends_with(b"\r\n\r\n") {
+                body = &body[..body.len() - 2];
             }
+            Cow::Borrowed(body)
+        }
+        DkimCanonicalizationType::Relaxed => {
+            let mut out = Vec::with_capacity(body.len());
+            loop {
+                match body {
+                    [b' ' | b'\t', b'\r', b'\n', ..] => {}
+                    [b' ' | b'\t', b' ' | b'\t', ..] => {}
+                    [b' ' | b'\t', ..] => out.push(b' '),
+                    [c, ..] => out.push(*c),
+                    [] => break,
+                }
+                body = &body[1..];
+            }
+            // Remove empty lines at end
+            while out.ends_with(b"\r\n\r\n") {
+                out.truncate(out.len() - 2);
+            }
+            Cow::Owned(out)
         }
     }
 }
 
-/// Canonicalize the value of an header
-fn dkim_canonicalize_header_value(
-    value: &str,
-    canonicalization: DkimCanonicalizationType,
-) -> Cow<'_, str> {
-    match canonicalization {
-        DkimCanonicalizationType::Simple => Cow::Borrowed(value),
-        DkimCanonicalizationType::Relaxed => {
-            static RE_EOL: Lazy<Regex> = Lazy::new(|| Regex::new("\r\n").unwrap());
-            static RE_SPACES: Lazy<Regex> = Lazy::new(|| Regex::new("[\\t ]+").unwrap());
-            let value = RE_EOL.replace_all(value, "");
-            Cow::Owned(format!(
-                "{}\r\n",
-                RE_SPACES.replace_all(&value, " ").trim_end()
-            ))
+fn dkim_canonicalize_headers_relaxed(headers: &str) -> String {
+    let mut r = String::with_capacity(headers.len());
+
+    fn skip_whitespace(h: &str) -> &str {
+        match h.as_bytes().first() {
+            Some(b' ' | b'\t') => skip_whitespace(&h[1..]),
+            _ => h,
         }
     }
+
+    fn name(h: &str, out: &mut String) {
+        if let Some(name_end) = h.bytes().position(|c| c == b':') {
+            let (name, rest) = h.split_at(name_end + 1);
+            *out += name;
+            // Space after header colon is stripped.
+            value(skip_whitespace(rest), out);
+        } else {
+            // This should never happen.
+            *out += h;
+        }
+    }
+
+    fn value(h: &str, out: &mut String) {
+        match h.as_bytes() {
+            // Continuation lines.
+            [b'\r', b'\n', b' ' | b'\t', ..] => {
+                out.push(' ');
+                value(skip_whitespace(&h[2..]), out);
+            }
+            // End of header.
+            [b'\r', b'\n', ..] => {
+                *out += "\r\n";
+                name(&h[2..], out)
+            }
+            // Sequential whitespace.
+            [b' ' | b'\t', b' ' | b'\t' | b'\r', ..] => value(&h[1..], out),
+            // All whitespace becomes spaces.
+            [b'\t', ..] => {
+                out.push(' ');
+                value(&h[1..], out)
+            }
+            [_, ..] => {
+                let mut chars = h.chars();
+                out.push(chars.next().unwrap());
+                value(chars.as_str(), out)
+            }
+            [] => {}
+        }
+    }
+
+    name(headers, &mut r);
+
+    r
 }
 
 /// Canonicalize header tag
@@ -277,56 +323,44 @@ fn dkim_canonicalize_headers<'a>(
     mail_headers: &Headers,
     canonicalization: DkimCanonicalizationType,
 ) -> String {
+    let mut covered_headers = Headers::new();
+    for name in headers_list {
+        if let Some(h) = mail_headers.find_header(name) {
+            let name = dkim_canonicalize_header_tag(name, canonicalization);
+            covered_headers.insert_raw(HeaderValue::dangerous_new_pre_encoded(
+                HeaderName::new_from_ascii(name.into()).unwrap(),
+                h.get_raw().into(),
+                h.get_encoded().into(),
+            ));
+        }
+    }
+
+    let serialized = covered_headers.to_string();
+
     match canonicalization {
-        DkimCanonicalizationType::Simple => {
-            let mut signed_headers = Headers::new();
-
-            for h in headers_list {
-                let h = dkim_canonicalize_header_tag(h, canonicalization);
-                if let Some(value) = mail_headers.get_raw(&h) {
-                    signed_headers.insert_raw(HeaderValue::new(
-                        HeaderName::new_from_ascii(h.into()).unwrap(),
-                        dkim_canonicalize_header_value(value, canonicalization).to_string(),
-                    ))
-                }
-            }
-
-            signed_headers.to_string()
-        }
-        DkimCanonicalizationType::Relaxed => {
-            let mut signed_headers = String::new();
-
-            for h in headers_list {
-                let h = dkim_canonicalize_header_tag(h, canonicalization);
-                if let Some(value) = mail_headers.get_raw(&h) {
-                    write!(
-                        signed_headers,
-                        "{}:{}",
-                        h,
-                        dkim_canonicalize_header_value(value, canonicalization)
-                    )
-                    .expect("write implementation returned an error")
-                }
-            }
-
-            signed_headers
-        }
+        DkimCanonicalizationType::Simple => serialized,
+        DkimCanonicalizationType::Relaxed => dkim_canonicalize_headers_relaxed(&serialized),
     }
 }
 
-/// Sign with Dkim a message by adding Dkim-Signture header created with configuration expressed by
+/// Sign with Dkim a message by adding Dkim-Signature header created with configuration expressed by
 /// dkim_config
-pub(super) fn dkim_sign(message: &mut Message, dkim_config: &DkimConfig) {
-    let timestamp = SystemTime::now()
+
+pub fn dkim_sign(message: &mut Message, dkim_config: &DkimConfig) {
+    dkim_sign_fixed_time(message, dkim_config, SystemTime::now())
+}
+
+fn dkim_sign_fixed_time(message: &mut Message, dkim_config: &DkimConfig, timestamp: SystemTime) {
+    let timestamp = timestamp
         .duration_since(SystemTime::UNIX_EPOCH)
         .unwrap()
         .as_secs();
     let headers = message.headers();
-    let body_hash = Sha256::digest(&dkim_canonicalize_body(
+    let body_hash = Sha256::digest(dkim_canonicalize_body(
         &message.body_raw(),
         dkim_config.canonicalization.body,
     ));
-    let bh = base64::encode(body_hash);
+    let bh = crate::base64::encode(body_hash);
     let mut signed_headers_list =
         dkim_config
             .headers
@@ -358,16 +392,13 @@ pub(super) fn dkim_sign(message: &mut Message, dkim_config: &DkimConfig) {
     hashed_headers.update(canonicalized_dkim_header.trim_end().as_bytes());
     let hashed_headers = hashed_headers.finalize();
     let signature = match &dkim_config.private_key.0 {
-        InnerDkimSigningKey::Rsa(private_key) => base64::encode(
+        InnerDkimSigningKey::Rsa(private_key) => crate::base64::encode(
             private_key
-                .sign(
-                    PaddingScheme::new_pkcs1v15_sign(Some(Hash::SHA2_256)),
-                    &hashed_headers,
-                )
+                .sign(Pkcs1v15Sign::new::<Sha256>(), &hashed_headers)
                 .unwrap(),
         ),
         InnerDkimSigningKey::Ed25519(private_key) => {
-            base64::encode(private_key.sign(&hashed_headers).to_bytes())
+            crate::base64::encode(private_key.sign(&hashed_headers).to_bytes())
         }
     };
     let dkim_header = dkim_header_format(
@@ -385,21 +416,47 @@ pub(super) fn dkim_sign(message: &mut Message, dkim_config: &DkimConfig) {
 
 #[cfg(test)]
 mod test {
-    use std::{
-        io::Write,
-        process::{Command, Stdio},
-    };
+    use pretty_assertions::assert_eq;
 
     use super::{
         super::{
             header::{HeaderName, HeaderValue},
             Header, Message,
         },
-        dkim_canonicalize_body, dkim_canonicalize_header_value, dkim_canonicalize_headers,
-        DkimCanonicalizationType, DkimConfig, DkimSigningAlgorithm, DkimSigningKey,
+        dkim_canonicalize_body, dkim_canonicalize_headers, dkim_sign_fixed_time,
+        DkimCanonicalization, DkimCanonicalizationType, DkimConfig, DkimSigningAlgorithm,
+        DkimSigningKey,
     };
     use crate::StdError;
 
+    const KEY_RSA: &str = "-----BEGIN RSA PRIVATE KEY-----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+-----END RSA PRIVATE KEY-----";
+
     #[derive(Clone)]
     struct TestHeader(String);
 
@@ -417,112 +474,143 @@ mod test {
         }
     }
 
-    #[test]
-    fn test_body_simple_canonicalize() {
-        let body = b"test\r\n\r\ntest   \ttest\r\n\r\n\r\n";
-        let expected: &[u8] = b"test\r\n\r\ntest   \ttest\r\n";
-        assert_eq!(
-            dkim_canonicalize_body(body, DkimCanonicalizationType::Simple),
-            expected
-        )
-    }
-    #[test]
-    fn test_body_relaxed_canonicalize() {
-        let body = b"test\r\n\r\ntest   \ttest\r\n\r\n\r\n";
-        let expected: &[u8] = b"test\r\n\r\ntest test\r\n";
-        assert_eq!(
-            dkim_canonicalize_body(body, DkimCanonicalizationType::Relaxed),
-            expected
-        )
-    }
-    #[test]
-    fn test_header_simple_canonicalize() {
-        let value = "test\r\n\r\ntest   \ttest\r\n";
-        let expected = "test\r\n\r\ntest   \ttest\r\n";
-        assert_eq!(
-            dkim_canonicalize_header_value(value, DkimCanonicalizationType::Simple),
-            expected
-        )
-    }
-    #[test]
-    fn test_header_relaxed_canonicalize() {
-        let value = "test\r\n\r\ntest   \ttest\r\n";
-        let expected = "testtest test\r\n";
-        assert_eq!(
-            dkim_canonicalize_header_value(value, DkimCanonicalizationType::Relaxed),
-            expected
-        )
-    }
-
     fn test_message() -> Message {
         Message::builder()
-            .from("Test <test+ezrz@example.net>".parse().unwrap())
+            .from("Test O'Leary <test+ezrz@example.net>".parse().unwrap())
             .to("Test2 <test2@example.org>".parse().unwrap())
-            .header(TestHeader("test  test very very long with spaces and extra spaces   \twill be folded to several lines ".to_string()))
+            .date(std::time::UNIX_EPOCH)
+            .header(TestHeader("test  test very very long with spaces and extra spaces   \twill be folded to several lines ".to_owned()))
             .subject("Test with utf-8 ë")
-            .body("test\r\n\r\ntest   \ttest\r\n\r\n\r\n".to_string()).unwrap()
+            .body("test\r\n\r\ntest   \ttest\r\n\r\n\r\n".to_owned()).unwrap()
     }
 
     #[test]
     fn test_headers_simple_canonicalize() {
         let message = test_message();
-        assert_eq!(dkim_canonicalize_headers(["From", "Test"], &message.headers, DkimCanonicalizationType::Simple),"From: Test <test+ezrz@example.net>\r\nTest: test  test very very long with spaces and extra spaces   \twill be \r\n folded to several lines \r\n")
+        dbg!(message.headers.to_string());
+        assert_eq!(dkim_canonicalize_headers(["From", "Test"], &message.headers, DkimCanonicalizationType::Simple), "From: =?utf-8?b?VGVzdCBPJ0xlYXJ5?= <test+ezrz@example.net>\r\nTest: test  test very very long with spaces and extra spaces   \twill be\r\n folded to several lines \r\n")
     }
+
     #[test]
     fn test_headers_relaxed_canonicalize() {
         let message = test_message();
-        assert_eq!(dkim_canonicalize_headers(["From", "Test"], &message.headers, DkimCanonicalizationType::Relaxed),"from:Test <test+ezrz@example.net>\r\ntest:test test very very long with spaces and extra spaces will be folded to several lines\r\n")
+        dbg!(message.headers.to_string());
+        assert_eq!(dkim_canonicalize_headers(["From", "Test"], &message.headers, DkimCanonicalizationType::Relaxed),"from:=?utf-8?b?VGVzdCBPJ0xlYXJ5?= <test+ezrz@example.net>\r\ntest:test test very very long with spaces and extra spaces will be folded to several lines\r\n")
     }
+
     #[test]
-    fn test_signature_rsa() {
+    fn test_body_simple_canonicalize() {
+        let body = b" C \r\nD \t E\r\n\r\n\r\n";
+        assert_eq!(
+            dkim_canonicalize_body(body, DkimCanonicalizationType::Simple).into_owned(),
+            b" C \r\nD \t E\r\n"
+        );
+    }
+
+    #[test]
+    fn test_body_relaxed_canonicalize() {
+        let body = b" C \r\nD \t E\r\n\tF\r\n\t\r\n\r\n\r\n";
+        assert_eq!(
+            dkim_canonicalize_body(body, DkimCanonicalizationType::Relaxed).into_owned(),
+            b" C\r\nD E\r\n F\r\n"
+        );
+    }
+
+    #[test]
+    fn test_signature_rsa_simple() {
         let mut message = test_message();
-        let key = "-----BEGIN RSA PRIVATE KEY-----
-MIIEpAIBAAKCAQEAz+FHbM8BwkBBz/Ux5OYLQ5Bp1HVuCHTP6Rr3HXTnome/2cGl
-/ze0tsmmFbCjjsS89MXbMGs9xJhjv18LmL1N0UTllblOizzVjorQyN4RwBOfG34j
-7SS56pwzrA738Ry8FAbL5InPWEgVzbOhXuTCs8yuzcqTnm4sH/csnIl7cMWeQkVn
-1FR9LKMtUG0fjhDPkdX0jx3qTX1L3Z7a7gX6geY191yNd9i9DvE2/+wMigMYz1LA
-ts4alk2g86MQhtbjc8AOR7EC15hSw37/lmamlunYLa3wC+PzHNMA8sAfnmkgNvip
-ssjh8LnelD9qn+VtsjQB5ppkeQx3TcUPvz5z+QIDAQABAoIBAQCzRa5ZEbSMlumq
-s+PRaOox3CrIRHUd6c8bUlvmFVllX1++JRhInvvD3ubSMcD7cIMb/D1o5jMgheMP
-uKHBmQ+w91+e3W30+gOZp/EiKRDZupIuHXxSGKgUwZx2N3pvfr5b7viLIKWllpTn
-DpCNy251rIDbjGX97Tk0X+8jGBVSTCxtruGJR5a+hz4t9Z7bz7JjZWcRNJC+VA+Q
-ATjnV7AHO1WR+0tAdPJaHsRLI7drKFSqTYq0As+MksZ40p7T6blZW8NUXA09fJRn
-3mP2TZdWjjfBXZje026v4T7TZl+TELKw5WirL/UJ8Zw8dGGV6EZvbfMacZuUB1YQ
-0vZnGe4BAoGBAO63xWP3OV8oLAMF90umuusPaQNSc6DnpjnP+sTAcXEYJA0Sa4YD
-y8dpTAdFJ4YvUQhLxtbZFK5Ih3x7ZhuerLSJiZiDPC2IJJb7j/812zQQriOi4mQ8
-bimxM4Nzql8FKGaXMppE5grFLsy8tw7neIM9KE4uwe9ajwJrRrOTUY8ZAoGBAN7t
-+xFeuhg4F9expyaPpCvKT2YNAdMcDzpm7GtLX292u+DQgBfg50Ur9XmbS+RPlx1W
-r2Sw3bTjRjJU9QnSZLL2w3hiii/wdaePI4SCaydHdLi4ZGz/pNUsUY+ck2pLptS0
-F7rL+s9MV9lUyhvX+pIh+O3idMWAdaymzs7ZlgfhAoGAVoFn2Wrscmw3Tr0puVNp
-JudFsbt+RU/Mr+SLRiNKuKX74nTLXBwiC1hAAd5wjTK2VaBIJPEzilikKFr7TIT6
-ps20e/0KoKFWSRROQTh9/+cPg8Bx88rmTNt3BGq00Ywn8M1XvAm9pyd/Zxf36kG9
-LSnLYlGVW6xgaIsBau+2vXkCgYAeChVdxtTutIhJ8U9ju9FUcUN3reMEDnDi3sGW
-x6ZJf8dbSN0p2o1vXbgLNejpD+x98JNbzxVg7Ysk9xu5whb9opC+ZRDX2uAPvxL7
-JRPJTDCnP3mQ0nXkn78xydh3Z1BIsyfLbPcT/eaMi4dcbyL9lARWEcDIaEHzDNsr
-NlioIQKBgQCXIZp5IBfG5WSXzFk8xvP4BUwHKEI5bttClBmm32K+vaSz8qO6ak6G
-4frg+WVopFg3HBHdK9aotzPEd0eHMXJv3C06Ynt2lvF+Rgi/kwGbkuq/mFVnmYYR
-Fz0TZ6sKrTAF3fdkN3bcQv6JG1CfnWENDGtekemwcCEA9v46/RsOfg==
------END RSA PRIVATE KEY-----";
-        let signing_key = DkimSigningKey::new(key.to_string(), DkimSigningAlgorithm::Rsa).unwrap();
-        message.sign(&DkimConfig::default_config(
-            "dkimtest".to_string(),
-            "example.org".to_string(),
-            signing_key,
-        ));
-        println!("{}", std::str::from_utf8(&message.formatted()).unwrap());
-        let mut verify_command = Command::new("dkimverify")
-            .stdin(Stdio::piped())
-            .spawn()
-            .expect("Fail to verify message signature");
-        let mut stdin = verify_command.stdin.take().expect("Failed to open stdin");
-        std::thread::spawn(move || {
-            stdin
-                .write_all(&message.formatted())
-                .expect("Failed to write to stdin");
-        });
-        assert!(verify_command
-            .wait()
-            .expect("Command did not run")
-            .success());
+        let signing_key = DkimSigningKey::new(KEY_RSA, DkimSigningAlgorithm::Rsa).unwrap();
+        dkim_sign_fixed_time(
+            &mut message,
+            &DkimConfig::new(
+                "dkimtest".to_owned(),
+                "example.org".to_owned(),
+                signing_key,
+                vec![
+                    HeaderName::new_from_ascii_str("Date"),
+                    HeaderName::new_from_ascii_str("From"),
+                    HeaderName::new_from_ascii_str("Subject"),
+                    HeaderName::new_from_ascii_str("To"),
+                ],
+                DkimCanonicalization {
+                    header: DkimCanonicalizationType::Simple,
+                    body: DkimCanonicalizationType::Simple,
+                },
+            ),
+            std::time::UNIX_EPOCH,
+        );
+        let signed = message.formatted();
+        let signed = std::str::from_utf8(&signed).unwrap();
+        assert_eq!(
+            signed,
+            std::concat!(
+                "From: =?utf-8?b?VGVzdCBPJ0xlYXJ5?= <test+ezrz@example.net>\r\n",
+                "To: Test2 <test2@example.org>\r\n",
+                "Date: Thu, 01 Jan 1970 00:00:00 +0000\r\n",
+                "Test: test  test very very long with spaces and extra spaces   \twill be\r\n",
+                " folded to several lines \r\n",
+                "Subject: Test with utf-8 =?utf-8?b?w6s=?=\r\n",
+                "Content-Transfer-Encoding: 7bit\r\n",
+                "DKIM-Signature: v=1; a=rsa-sha256; d=example.org; s=dkimtest;\r\n",
+                " c=simple/simple; q=dns/txt; t=0; h=Date:From:Subject:To;\r\n",
+                " bh=f3Zksdcjqa/xRBwdyFzIXWCcgP7XTgxjCgYsXOMKQl4=;\r\n",
+                " b=NhoIMMAALoSgu5lKAR0+MUQunOWnU7wpF9ORUFtpxq9sGZDo9AX43AMhFemyM5W204jpFwMU6pm7AMR1nOYBdSYye4yUALtvT2nqbJBwSh7JeYu+z22t1RFKp7qQR1il8aSrkbZuNMFHYuSEwW76QtKwcNqP4bQOzS9CzgQp0ABu8qwYPBr/EypykPTfqjtyN+ywrfdqjjGOzTpRGolH0hc3CrAETNjjHbNBgKgucXmXTN7hMRdzqWjeFPxizXwouwNAavFClPG0l33gXVArFWn+CkgA84G/s4zuJiF7QPZR87Pu4pw/vIlSXxH4a42W3tT19v9iBTH7X7ldYegtmQ==\r\n",
+                "\r\n",
+                "test\r\n",
+                "\r\n",
+                "test   \ttest\r\n",
+                "\r\n",
+                "\r\n",
+            )
+        );
+    }
+
+    #[test]
+    fn test_signature_rsa_relaxed() {
+        let mut message = test_message();
+        let signing_key = DkimSigningKey::new(KEY_RSA, DkimSigningAlgorithm::Rsa).unwrap();
+        dkim_sign_fixed_time(
+            &mut message,
+            &DkimConfig::new(
+                "dkimtest".to_owned(),
+                "example.org".to_owned(),
+                signing_key,
+                vec![
+                    HeaderName::new_from_ascii_str("Date"),
+                    HeaderName::new_from_ascii_str("From"),
+                    HeaderName::new_from_ascii_str("Subject"),
+                    HeaderName::new_from_ascii_str("To"),
+                ],
+                DkimCanonicalization {
+                    header: DkimCanonicalizationType::Relaxed,
+                    body: DkimCanonicalizationType::Relaxed,
+                },
+            ),
+            std::time::UNIX_EPOCH,
+        );
+        let signed = message.formatted();
+        let signed = std::str::from_utf8(&signed).unwrap();
+        println!("{signed}");
+        assert_eq!(
+            signed,
+            std::concat!(
+                "From: =?utf-8?b?VGVzdCBPJ0xlYXJ5?= <test+ezrz@example.net>\r\n",
+                "To: Test2 <test2@example.org>\r\n",
+                "Date: Thu, 01 Jan 1970 00:00:00 +0000\r\n",
+                "Test: test  test very very long with spaces and extra spaces   \twill be\r\n",
+                " folded to several lines \r\n","Subject: Test with utf-8 =?utf-8?b?w6s=?=\r\n",
+                "Content-Transfer-Encoding: 7bit\r\n",
+                "DKIM-Signature: v=1; a=rsa-sha256; d=example.org; s=dkimtest;\r\n",
+                " c=relaxed/relaxed; q=dns/txt; t=0; h=date:from:subject:to;\r\n",
+                " bh=qN8je6qJgWFGSnN2MycC/XKPbN6BOrMJyAX2h4m19Ss=;\r\n",
+                " b=YaVfmH8dbGEywoLJ4uhbvYqDyQG1UGKFH3PE7zXGgk+YFxUgkwWjoA3aQupDNQtfTjfUsNe0dnrjyZP+ylnESpZBpbCIf5/n3FEh6j3RQthqNbQblcfH/U8mazTuRbVjYBbTZQDaQCMPTz+8D+ZQfXo2oq6dGzTuGvmuYft0CVsq/BIp/EkhZHqiphDeVJSHD4iKW8+L2XwEWThoY92xOYc1G0TtBwz2UJgtiHX2YulH/kRBHeK3dKn9RTNVL3VZ+9ZrnFwIhET9TPGtU2I+q0EMSWF9H9bTrASMgW/U+E0VM2btqJlrTU6rQ7wlQeHdwecLnzXcyhCUInF1+veMNw==\r\n",
+                "\r\n",
+                "test\r\n",
+                "\r\n",
+                "test   \ttest\r\n",
+                "\r\n",
+                "\r\n",
+            )
+        );
     }
 }

src/message/header/content.rs

@@ -13,12 +13,14 @@ use crate::BoxError;
 /// use-caches this header shouldn't be set manually.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[derive(Default)]
 pub enum ContentTransferEncoding {
     /// ASCII
     SevenBit,
     /// Quoted-Printable encoding
     QuotedPrintable,
     /// base64 encoding
+    #[default]
     Base64,
     /// Requires `8BITMIME`
     EightBit,
@@ -67,14 +69,10 @@ impl FromStr for ContentTransferEncoding {
     }
 }
 
-impl Default for ContentTransferEncoding {
-    fn default() -> Self {
-        ContentTransferEncoding::Base64
-    }
-}
-
 #[cfg(test)]
 mod test {
+    use pretty_assertions::assert_eq;
+
     use super::ContentTransferEncoding;
     use crate::message::header::{HeaderName, HeaderValue, Headers};
 
@@ -97,7 +95,7 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Transfer-Encoding"),
-            "7bit".to_string(),
+            "7bit".to_owned(),
         ));
 
         assert_eq!(
@@ -107,7 +105,7 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Transfer-Encoding"),
-            "base64".to_string(),
+            "base64".to_owned(),
         ));
 
         assert_eq!(

src/message/header/content_disposition.rs

@@ -16,13 +16,13 @@ impl ContentDisposition {
     pub fn inline() -> Self {
         Self(HeaderValue::dangerous_new_pre_encoded(
             Self::name(),
-            "inline".to_string(),
-            "inline".to_string(),
+            "inline".to_owned(),
+            "inline".to_owned(),
         ))
     }
 
     /// An attachment which should be displayed inline into the message, but that also
-    /// species the filename in case it were to be downloaded
+    /// species the filename in case it is downloaded
     pub fn inline_with_name(file_name: &str) -> Self {
         Self::with_name("inline", file_name)
     }
@@ -33,17 +33,19 @@ impl ContentDisposition {
     }
 
     fn with_name(kind: &str, file_name: &str) -> Self {
-        let raw_value = format!("{}; filename=\"{}\"", kind, file_name);
+        let raw_value = format!("{kind}; filename=\"{file_name}\"");
 
         let mut encoded_value = String::new();
         let line_len = "Content-Disposition: ".len();
-        let mut w = EmailWriter::new(&mut encoded_value, line_len, false);
-        w.write_str(kind).expect("writing `kind` returned an error");
-        w.write_char(';').expect("writing `;` returned an error");
-        w.space();
+        {
+            let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false, false);
+            w.write_str(kind).expect("writing `kind` returned an error");
+            w.write_char(';').expect("writing `;` returned an error");
+            w.optional_breakpoint();
 
-        email_encoding::headers::rfc2231::encode("filename", file_name, &mut w)
-            .expect("some Write implementation returned an error");
+            email_encoding::headers::rfc2231::encode("filename", file_name, &mut w)
+                .expect("some Write implementation returned an error");
+        }
 
         Self(HeaderValue::dangerous_new_pre_encoded(
             Self::name(),
@@ -77,6 +79,8 @@ impl Header for ContentDisposition {
 
 #[cfg(test)]
 mod test {
+    use pretty_assertions::assert_eq;
+
     use super::ContentDisposition;
     use crate::message::header::{HeaderName, HeaderValue, Headers};
 
@@ -86,12 +90,12 @@ mod test {
 
         headers.set(ContentDisposition::inline());
 
-        assert_eq!(format!("{}", headers), "Content-Disposition: inline\r\n");
+        assert_eq!(format!("{headers}"), "Content-Disposition: inline\r\n");
 
         headers.set(ContentDisposition::attachment("something.txt"));
 
         assert_eq!(
-            format!("{}", headers),
+            format!("{headers}"),
             "Content-Disposition: attachment; filename=\"something.txt\"\r\n"
         );
     }
@@ -102,7 +106,7 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Disposition"),
-            "inline".to_string(),
+            "inline".to_owned(),
         ));
 
         assert_eq!(
@@ -112,7 +116,7 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Disposition"),
-            "attachment; filename=\"something.txt\"".to_string(),
+            "attachment; filename=\"something.txt\"".to_owned(),
         ));
 
         assert_eq!(

src/message/header/content_type.rs

@@ -11,12 +11,12 @@ use crate::BoxError;
 
 /// `Content-Type` of the body
 ///
-/// This struct can represent any valid [mime type], which can be parsed via
+/// This struct can represent any valid [MIME type], which can be parsed via
 /// [`ContentType::parse`]. Constants are provided for the most-used mime-types.
 ///
 /// Defined in [RFC2045](https://tools.ietf.org/html/rfc2045#section-5)
 ///
-/// [mime type]: https://www.iana.org/assignments/media-types/media-types.xhtml
+/// [MIME type]: https://www.iana.org/assignments/media-types/media-types.xhtml
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ContentType(Mime);
 
@@ -135,8 +135,7 @@ mod serde {
                     match ContentType::parse(mime) {
                         Ok(content_type) => Ok(content_type),
                         Err(_) => Err(E::custom(format!(
-                            "Couldn't parse the following MIME-Type: {}",
-                            mime
+                            "Couldn't parse the following MIME-Type: {mime}"
                         ))),
                     }
                 }
@@ -149,6 +148,8 @@ mod serde {
 
 #[cfg(test)]
 mod test {
+    use pretty_assertions::assert_eq;
+
     use super::ContentType;
     use crate::message::header::{HeaderName, HeaderValue, Headers};
 
@@ -177,14 +178,14 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Type"),
-            "text/plain; charset=utf-8".to_string(),
+            "text/plain; charset=utf-8".to_owned(),
         ));
 
         assert_eq!(headers.get::<ContentType>(), Some(ContentType::TEXT_PLAIN));
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Type"),
-            "text/html; charset=utf-8".to_string(),
+            "text/html; charset=utf-8".to_owned(),
         ));
 
         assert_eq!(headers.get::<ContentType>(), Some(ContentType::TEXT_HTML));

src/message/header/date.rs

@@ -8,7 +8,7 @@ use crate::BoxError;
 /// Message `Date` header
 ///
 /// Defined in [RFC2822](https://tools.ietf.org/html/rfc2822#section-3.3)
-#[derive(Debug, Clone, Copy, PartialEq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct Date(HttpDate);
 
 impl Date {
@@ -74,6 +74,8 @@ impl From<Date> for SystemTime {
 mod test {
     use std::time::{Duration, SystemTime};
 
+    use pretty_assertions::assert_eq;
+
     use super::Date;
     use crate::message::header::{HeaderName, HeaderValue, Headers};
 
@@ -88,7 +90,7 @@ mod test {
 
         assert_eq!(
             headers.to_string(),
-            "Date: Tue, 15 Nov 1994 08:12:31 +0000\r\n".to_string()
+            "Date: Tue, 15 Nov 1994 08:12:31 +0000\r\n".to_owned()
         );
 
         // Tue, 15 Nov 1994 08:12:32 GMT
@@ -108,7 +110,7 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Date"),
-            "Tue, 15 Nov 1994 08:12:31 +0000".to_string(),
+            "Tue, 15 Nov 1994 08:12:31 +0000".to_owned(),
         ));
 
         assert_eq!(
@@ -120,7 +122,7 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Date"),
-            "Tue, 15 Nov 1994 08:12:32 +0000".to_string(),
+            "Tue, 15 Nov 1994 08:12:32 +0000".to_owned(),
         ));
 
         assert_eq!(

src/message/header/mailbox.rs

@@ -14,7 +14,7 @@ pub trait MailboxesHeader {
 macro_rules! mailbox_header {
     ($(#[$doc:meta])*($type_name: ident, $header_name: expr)) => {
         $(#[$doc])*
-        #[derive(Debug, Clone, PartialEq)]
+        #[derive(Debug, Clone, PartialEq, Eq)]
         pub struct $type_name(Mailbox);
 
         impl Header for $type_name {
@@ -30,8 +30,10 @@ macro_rules! mailbox_header {
             fn display(&self) -> HeaderValue {
                 let mut encoded_value = String::new();
                 let line_len = $header_name.len() + ": ".len();
-                let mut w = EmailWriter::new(&mut encoded_value, line_len, false);
-                self.0.encode(&mut w).expect("writing `Mailbox` returned an error");
+                {
+                    let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false, false);
+                    self.0.encode(&mut w).expect("writing `Mailbox` returned an error");
+                }
 
                 HeaderValue::dangerous_new_pre_encoded(Self::name(), self.0.to_string(), encoded_value)
             }
@@ -56,7 +58,7 @@ macro_rules! mailbox_header {
 macro_rules! mailboxes_header {
     ($(#[$doc:meta])*($type_name: ident, $header_name: expr)) => {
         $(#[$doc])*
-        #[derive(Debug, Clone, PartialEq)]
+        #[derive(Debug, Clone, PartialEq, Eq)]
         pub struct $type_name(pub(crate) Mailboxes);
 
         impl MailboxesHeader for $type_name {
@@ -78,8 +80,10 @@ macro_rules! mailboxes_header {
             fn display(&self) -> HeaderValue {
                 let mut encoded_value = String::new();
                 let line_len = $header_name.len() + ": ".len();
-                let mut w = EmailWriter::new(&mut encoded_value, line_len, false);
-                self.0.encode(&mut w).expect("writing `Mailboxes` returned an error");
+                {
+                    let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false, false);
+                    self.0.encode(&mut w).expect("writing `Mailboxes` returned an error");
+                }
 
                 HeaderValue::dangerous_new_pre_encoded(Self::name(), self.0.to_string(), encoded_value)
             }
@@ -172,6 +176,8 @@ mailboxes_header! {
 
 #[cfg(test)]
 mod test {
+    use pretty_assertions::assert_eq;
+
     use super::{From, Mailbox, Mailboxes};
     use crate::message::header::{HeaderName, HeaderValue, Headers};
 
@@ -246,7 +252,7 @@ mod test {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("From"),
-            "kayo@example.com".to_string(),
+            "kayo@example.com".to_owned(),
         ));
 
         assert_eq!(headers.get::<From>(), Some(From(from)));
@@ -259,7 +265,7 @@ mod test {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("From"),
-            "K. <kayo@example.com>".to_string(),
+            "K. <kayo@example.com>".to_owned(),
         ));
 
         assert_eq!(headers.get::<From>(), Some(From(from)));
@@ -275,7 +281,7 @@ mod test {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("From"),
-            "kayo@example.com, pony@domain.tld".to_string(),
+            "kayo@example.com, pony@domain.tld".to_owned(),
         ));
 
         assert_eq!(headers.get::<From>(), Some(From(from.into())));
@@ -291,7 +297,7 @@ mod test {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("From"),
-            "K. <kayo@example.com>, Pony P. <pony@domain.tld>".to_string(),
+            "K. <kayo@example.com>, Pony P. <pony@domain.tld>".to_owned(),
         ));
 
         assert_eq!(headers.get::<From>(), Some(From(from.into())));
@@ -300,14 +306,30 @@ mod test {
     #[test]
     fn parse_multi_with_name_containing_comma() {
         let from: Vec<Mailbox> = vec![
-            "Test, test <1@example.com>".parse().unwrap(),
-            "Test2, test2 <2@example.com>".parse().unwrap(),
+            "\"Test, test\" <1@example.com>".parse().unwrap(),
+            "\"Test2, test2\" <2@example.com>".parse().unwrap(),
         ];
 
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("From"),
-            "Test, test <1@example.com>, Test2, test2 <2@example.com>".to_string(),
+            "\"Test, test\" <1@example.com>, \"Test2, test2\" <2@example.com>".to_owned(),
+        ));
+
+        assert_eq!(headers.get::<From>(), Some(From(from.into())));
+    }
+
+    #[test]
+    fn parse_multi_with_name_containing_double_quotes() {
+        let from: Vec<Mailbox> = vec![
+            "\"Test, test\" <1@example.com>".parse().unwrap(),
+            "\"Test2, \"test2\"\" <2@example.com>".parse().unwrap(),
+        ];
+
+        let mut headers = Headers::new();
+        headers.insert_raw(HeaderValue::new(
+            HeaderName::new_from_ascii_str("From"),
+            "\"Test, test\" <1@example.com>, \"Test2, \"test2\"\" <2@example.com>".to_owned(),
         ));
 
         assert_eq!(headers.get::<From>(), Some(From(from.into())));
@@ -318,9 +340,20 @@ mod test {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("From"),
-            "Test, test <1@example.com>, Test2, test2".to_string(),
+            "\"Test, test\" <1@example.com>, \"Test2, test2\"".to_owned(),
         ));
 
         assert_eq!(headers.get::<From>(), None);
     }
+
+    #[test]
+    fn mailbox_format_address_with_angle_bracket() {
+        assert_eq!(
+            format!(
+                "{}",
+                Mailbox::new(Some("<3".into()), "i@love.example".parse().unwrap())
+            ),
+            r#""<3" <i@love.example>"#
+        );
+    }
 }

src/message/header/mod.rs

@@ -3,10 +3,12 @@
 use std::{
     borrow::Cow,
     error::Error,
-    fmt::{self, Display, Formatter},
+    fmt::{self, Display, Formatter, Write},
     ops::Deref,
 };
 
+use email_encoding::headers::EmailWriter;
+
 pub use self::{
     content::*,
     content_disposition::ContentDisposition,
@@ -64,7 +66,7 @@ impl Headers {
         }
     }
 
-    /// Returns a copy of an `Header` present in `Headers`
+    /// Returns a copy of a `Header` present in `Headers`
     ///
     /// Returns `None` if `Header` isn't present in `Headers`.
     pub fn get<H: Header>(&self) -> Option<H> {
@@ -121,7 +123,7 @@ impl Headers {
         self.find_header_index(name).map(|i| self.headers.remove(i))
     }
 
-    fn find_header(&self, name: &str) -> Option<&HeaderValue> {
+    pub(crate) fn find_header(&self, name: &str) -> Option<&HeaderValue> {
         self.headers
             .iter()
             .find(|value| name.eq_ignore_ascii_case(&value.name))
@@ -275,6 +277,7 @@ impl PartialEq<HeaderName> for &str {
     }
 }
 
+/// A safe for use header value
 #[derive(Debug, Clone, PartialEq)]
 pub struct HeaderValue {
     name: HeaderName,
@@ -283,6 +286,12 @@ pub struct HeaderValue {
 }
 
 impl HeaderValue {
+    /// Construct a new `HeaderValue` and encode it
+    ///
+    /// Takes the header `name` and the `raw_value` and encodes
+    /// it via `RFC2047` and line folds it.
+    ///
+    /// [`RFC2047`]: https://datatracker.ietf.org/doc/html/rfc2047
     pub fn new(name: HeaderName, raw_value: String) -> Self {
         let mut encoded_value = String::with_capacity(raw_value.len());
         HeaderValueEncoder::encode(&name, &raw_value, &mut encoded_value).unwrap();
@@ -294,6 +303,14 @@ impl HeaderValue {
         }
     }
 
+    /// Construct a new `HeaderValue` using a pre-encoded header value
+    ///
+    /// This method is _extremely_ dangerous as it opens up
+    /// the encoder to header injection attacks, but is sometimes
+    /// acceptable for use if `encoded_value` contains only ascii
+    /// printable characters and is already line folded.
+    ///
+    /// When in doubt, use [`HeaderValue::new`].
     pub fn dangerous_new_pre_encoded(
         name: HeaderName,
         raw_value: String,
@@ -305,57 +322,41 @@ impl HeaderValue {
             encoded_value,
         }
     }
+
+    #[cfg(feature = "dkim")]
+    pub(crate) fn get_raw(&self) -> &str {
+        &self.raw_value
+    }
+
+    #[cfg(feature = "dkim")]
+    pub(crate) fn get_encoded(&self) -> &str {
+        &self.encoded_value
+    }
 }
 
-const ENCODING_START_PREFIX: &str = "=?utf-8?b?";
-const ENCODING_END_SUFFIX: &str = "?=";
-const MAX_LINE_LEN: usize = 76;
-
 /// [RFC 1522](https://tools.ietf.org/html/rfc1522) header value encoder
-struct HeaderValueEncoder {
-    line_len: usize,
+struct HeaderValueEncoder<'a> {
+    writer: EmailWriter<'a>,
     encode_buf: String,
 }
 
-impl HeaderValueEncoder {
-    fn encode(name: &str, value: &str, f: &mut impl fmt::Write) -> fmt::Result {
-        let (words_iter, encoder) = Self::new(name, value);
-        encoder.format(words_iter, f)
+impl<'a> HeaderValueEncoder<'a> {
+    fn encode(name: &str, value: &'a str, f: &'a mut impl fmt::Write) -> fmt::Result {
+        let encoder = Self::new(name, f);
+        encoder.format(value.split_inclusive(' '))
     }
 
-    fn new<'a>(name: &str, value: &'a str) -> (WordsPlusFillIterator<'a>, Self) {
-        (
-            WordsPlusFillIterator { s: value },
-            Self {
-                line_len: name.len() + ": ".len(),
-                encode_buf: String::new(),
-            },
-        )
+    fn new(name: &str, writer: &'a mut dyn Write) -> Self {
+        let line_len = name.len() + ": ".len();
+        let writer = EmailWriter::new(writer, line_len, 0, false, false);
+
+        Self {
+            writer,
+            encode_buf: String::new(),
+        }
     }
 
-    fn format(
-        mut self,
-        words_iter: WordsPlusFillIterator<'_>,
-        f: &mut impl fmt::Write,
-    ) -> fmt::Result {
-        /// Estimate if an encoded string of `len` would fix in an empty line
-        fn would_fit_new_line(len: usize) -> bool {
-            len < (MAX_LINE_LEN - " ".len())
-        }
-
-        /// Estimate how long a string of `len` would be after base64 encoding plus
-        /// adding the encoding prefix and suffix to it
-        fn base64_len(len: usize) -> usize {
-            ENCODING_START_PREFIX.len() + (len * 4 / 3 + 4) + ENCODING_END_SUFFIX.len()
-        }
-
-        /// Estimate how many more bytes we can fit in the current line
-        fn available_len_to_max_encode_len(len: usize) -> usize {
-            len.saturating_sub(
-                ENCODING_START_PREFIX.len() + (len * 3 / 4 + 4) + ENCODING_END_SUFFIX.len(),
-            )
-        }
-
+    fn format(mut self, words_iter: impl Iterator<Item = &'a str>) -> fmt::Result {
         for next_word in words_iter {
             let allowed = allowed_str(next_word);
 
@@ -363,205 +364,54 @@ impl HeaderValueEncoder {
                 // This word only contains allowed characters
 
                 // the next word is allowed, but we may have accumulated some words to encode
-                self.flush_encode_buf(f, true)?;
+                self.flush_encode_buf()?;
 
-                if next_word.len() > self.remaining_line_len() {
-                    // not enough space left on this line to encode word
-
-                    if self.something_written_to_this_line() && would_fit_new_line(next_word.len())
-                    {
-                        // word doesn't fit this line, but something had already been written to it,
-                        // and word would fit the next line, so go to a new line
-                        // so go to new line
-                        self.new_line(f)?;
-                    } else {
-                        // word neither fits this line and the next one, cut it
-                        // in the middle and make it fit
-
-                        let mut next_word = next_word;
-
-                        while !next_word.is_empty() {
-                            if self.remaining_line_len() == 0 {
-                                self.new_line(f)?;
-                            }
-
-                            let len = self.remaining_line_len().min(next_word.len());
-                            let first_part = &next_word[..len];
-                            next_word = &next_word[len..];
-
-                            f.write_str(first_part)?;
-                            self.line_len += first_part.len();
-                        }
-
-                        continue;
-                    }
-                }
-
-                // word fits, write it!
-                f.write_str(next_word)?;
-                self.line_len += next_word.len();
+                self.writer.folding().write_str(next_word)?;
             } else {
                 // This word contains unallowed characters
-
-                if self.remaining_line_len() >= base64_len(self.encode_buf.len() + next_word.len())
-                {
-                    // next_word fits
-                    self.encode_buf.push_str(next_word);
-                    continue;
-                }
-
-                // next_word doesn't fit this line
-
-                if would_fit_new_line(base64_len(next_word.len())) {
-                    // ...but it would fit the next one
-
-                    self.flush_encode_buf(f, false)?;
-                    self.new_line(f)?;
-
-                    self.encode_buf.push_str(next_word);
-                    continue;
-                }
-
-                // ...and also wouldn't fit the next one.
-                // chop it up into pieces
-
-                let mut next_word = next_word;
-
-                while !next_word.is_empty() {
-                    let mut len = available_len_to_max_encode_len(self.remaining_line_len())
-                        .min(next_word.len());
-
-                    if len == 0 {
-                        self.flush_encode_buf(f, false)?;
-                        self.new_line(f)?;
-                    }
-
-                    // avoid slicing on a char boundary
-                    while !next_word.is_char_boundary(len) {
-                        len += 1;
-                    }
-                    let first_part = &next_word[..len];
-                    next_word = &next_word[len..];
-
-                    self.encode_buf.push_str(first_part);
-                }
+                self.encode_buf.push_str(next_word);
             }
         }
 
-        self.flush_encode_buf(f, false)?;
+        self.flush_encode_buf()?;
 
         Ok(())
     }
 
-    /// Returns the number of bytes left for the current line
-    fn remaining_line_len(&self) -> usize {
-        MAX_LINE_LEN - self.line_len
-    }
-
-    /// Returns true if something has been written to the current line
-    fn something_written_to_this_line(&self) -> bool {
-        self.line_len > 1
-    }
-
-    fn flush_encode_buf(
-        &mut self,
-        f: &mut impl fmt::Write,
-        switching_to_allowed: bool,
-    ) -> fmt::Result {
+    fn flush_encode_buf(&mut self) -> fmt::Result {
         if self.encode_buf.is_empty() {
             // nothing to encode
             return Ok(());
         }
 
-        let mut write_after = None;
+        let prefix = self.encode_buf.trim_end_matches(' ');
+        email_encoding::headers::rfc2047::encode(prefix, &mut self.writer)?;
 
-        if switching_to_allowed {
-            // If the next word only contains allowed characters, and the string to encode
-            // ends with a space, take the space out of the part to encode
-
-            let last_char = self.encode_buf.pop().expect("self.encode_buf isn't empty");
-            if is_space_like(last_char) {
-                write_after = Some(last_char);
-            } else {
-                self.encode_buf.push(last_char);
-            }
-        }
-
-        f.write_str(ENCODING_START_PREFIX)?;
-        let encoded = base64::display::Base64Display::with_config(
-            self.encode_buf.as_bytes(),
-            base64::STANDARD,
-        );
-        write!(f, "{}", encoded)?;
-        f.write_str(ENCODING_END_SUFFIX)?;
-
-        self.line_len += ENCODING_START_PREFIX.len();
-        self.line_len += self.encode_buf.len() * 4 / 3 + 4;
-        self.line_len += ENCODING_END_SUFFIX.len();
-
-        if let Some(write_after) = write_after {
-            f.write_char(write_after)?;
-            self.line_len += 1;
+        // TODO: add a better API for doing this in email-encoding
+        let spaces = self.encode_buf.len() - prefix.len();
+        for _ in 0..spaces {
+            self.writer.space();
         }
 
         self.encode_buf.clear();
         Ok(())
     }
-
-    fn new_line(&mut self, f: &mut impl fmt::Write) -> fmt::Result {
-        f.write_str("\r\n ")?;
-        self.line_len = 1;
-
-        Ok(())
-    }
-}
-
-/// Iterator yielding a string split space by space, but including all space
-/// characters between it and the next word
-struct WordsPlusFillIterator<'a> {
-    s: &'a str,
-}
-
-impl<'a> Iterator for WordsPlusFillIterator<'a> {
-    type Item = &'a str;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        if self.s.is_empty() {
-            return None;
-        }
-
-        let next_word = self
-            .s
-            .char_indices()
-            .skip(1)
-            .skip_while(|&(_i, c)| !is_space_like(c))
-            .find(|&(_i, c)| !is_space_like(c))
-            .map(|(i, _)| i);
-
-        let word = &self.s[..next_word.unwrap_or(self.s.len())];
-        self.s = &self.s[word.len()..];
-        Some(word)
-    }
-}
-
-const fn is_space_like(c: char) -> bool {
-    c == ',' || c == ' '
 }
 
 fn allowed_str(s: &str) -> bool {
-    s.chars().all(allowed_char)
+    s.bytes().all(allowed_char)
 }
 
-const fn allowed_char(c: char) -> bool {
-    c >= 1 as char && c <= 9 as char
-        || c == 11 as char
-        || c == 12 as char
-        || c >= 14 as char && c <= 127 as char
+const fn allowed_char(c: u8) -> bool {
+    c >= 1 && c <= 9 || c == 11 || c == 12 || c >= 14 && c <= 127
 }
 
 #[cfg(test)]
 mod tests {
-    use super::{HeaderName, HeaderValue, Headers};
+    use pretty_assertions::assert_eq;
+
+    use super::{HeaderName, HeaderValue, Headers, To};
+    use crate::message::Mailboxes;
 
     #[test]
     fn valid_headername() {
@@ -624,7 +474,7 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("To"),
-            "John Doe <example@example.com>, Jean Dupont <jean@example.com>".to_string(),
+            "John Doe <example@example.com>, Jean Dupont <jean@example.com>".to_owned(),
         ));
 
         assert_eq!(
@@ -638,14 +488,14 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("To"),
-            "Ascii <example@example.com>, John Doe <johndoe@example.com, John Smith <johnsmith@example.com>, Pinco Pallino <pincopallino@example.com>, Jemand <jemand@example.com>, Jean Dupont <jean@example.com>".to_string(),
+            "Ascii <example@example.com>, John Doe <johndoe@example.com, John Smith <johnsmith@example.com>, Pinco Pallino <pincopallino@example.com>, Jemand <jemand@example.com>, Jean Dupont <jean@example.com>".to_owned(),
         ));
 
         assert_eq!(
             headers.to_string(),
             concat!(
-                "To: Ascii <example@example.com>, John Doe <johndoe@example.com, John Smith \r\n",
-                " <johnsmith@example.com>, Pinco Pallino <pincopallino@example.com>, Jemand \r\n",
+                "To: Ascii <example@example.com>, John Doe <johndoe@example.com, John Smith\r\n",
+                " <johnsmith@example.com>, Pinco Pallino <pincopallino@example.com>, Jemand\r\n",
                 " <jemand@example.com>, Jean Dupont <jean@example.com>\r\n"
             )
         );
@@ -656,14 +506,14 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "Hello! This is lettre, and this IsAVeryLongLineDoYouKnowWhatsGoingToHappenIGuessWeAreGoingToFindOut. Ok I guess that's it!".to_string()
+            "Hello! This is lettre, and this IsAVeryLongLineDoYouKnowWhatsGoingToHappenIGuessWeAreGoingToFindOut. Ok I guess that's it!".to_owned()
         ));
 
         assert_eq!(
             headers.to_string(),
             concat!(
-                "Subject: Hello! This is lettre, and this \r\n ",
-                "IsAVeryLongLineDoYouKnowWhatsGoingToHappenIGuessWeAreGoingToFindOut. Ok I \r\n",
+                "Subject: Hello! This is lettre, and this\r\n",
+                " IsAVeryLongLineDoYouKnowWhatsGoingToHappenIGuessWeAreGoingToFindOut. Ok I\r\n",
                 " guess that's it!\r\n"
             )
         );
@@ -675,14 +525,15 @@ mod tests {
         headers.insert_raw(
             HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "Hello! IGuessTheLastLineWasntLongEnoughSoLetsTryAgainShallWeWhatDoYouThinkItsGoingToHappenIGuessWereAboutToFindOut! I don't know".to_string()
+            "Hello! IGuessTheLastLineWasntLongEnoughSoLetsTryAgainShallWeWhatDoYouThinkItsGoingToHappenIGuessWereAboutToFindOut! I don't know".to_owned()
         ));
 
         assert_eq!(
             headers.to_string(),
             concat!(
-                "Subject: Hello! IGuessTheLastLineWasntLongEnoughSoLetsTryAgainShallWeWhatDoY\r\n",
-                " ouThinkItsGoingToHappenIGuessWereAboutToFindOut! I don't know\r\n",
+                "Subject: Hello!\r\n",
+                " IGuessTheLastLineWasntLongEnoughSoLetsTryAgainShallWeWhatDoYouThinkItsGoingToHappenIGuessWereAboutToFindOut!\r\n",
+                " I don't know\r\n",
             )
         );
     }
@@ -692,16 +543,12 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "1abcdefghijklmnopqrstuvwxyz2abcdefghijklmnopqrstuvwxyz3abcdefghijklmnopqrstuvwxyz4abcdefghijklmnopqrstuvwxyz5abcdefghijklmnopqrstuvwxyz6abcdefghijklmnopqrstuvwxyz".to_string()
+            "1abcdefghijklmnopqrstuvwxyz2abcdefghijklmnopqrstuvwxyz3abcdefghijklmnopqrstuvwxyz4abcdefghijklmnopqrstuvwxyz5abcdefghijklmnopqrstuvwxyz6abcdefghijklmnopqrstuvwxyz".to_owned()
         ));
 
         assert_eq!(
             headers.to_string(),
-            concat!(
-                "Subject: 1abcdefghijklmnopqrstuvwxyz2abcdefghijklmnopqrstuvwxyz3abcdefghijkl\r\n",
-                " mnopqrstuvwxyz4abcdefghijklmnopqrstuvwxyz5abcdefghijklmnopqrstuvwxyz6abcdef\r\n",
-                " ghijklmnopqrstuvwxyz\r\n",
-            )
+            "Subject: 1abcdefghijklmnopqrstuvwxyz2abcdefghijklmnopqrstuvwxyz3abcdefghijklmnopqrstuvwxyz4abcdefghijklmnopqrstuvwxyz5abcdefghijklmnopqrstuvwxyz6abcdefghijklmnopqrstuvwxyz\r\n",
         );
     }
 
@@ -710,7 +557,7 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("To"),
-            "Seán <sean@example.com>".to_string(),
+            "Seán <sean@example.com>".to_owned(),
         ));
 
         assert_eq!(
@@ -724,7 +571,7 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("To"),
-            "🌎 <world@example.com>".to_string(),
+            "🌎 <world@example.com>".to_owned(),
         ));
 
         assert_eq!(
@@ -736,19 +583,46 @@ mod tests {
     #[test]
     fn format_special_with_folding() {
         let mut headers = Headers::new();
-        headers.insert_raw(HeaderValue::new(
-            HeaderName::new_from_ascii_str("To"),
-            "🌍 <world@example.com>, 🦆 Everywhere <ducks@example.com>, Иванов Иван Иванович <ivanov@example.com>, Jānis Bērziņš <janis@example.com>, Seán Ó Rudaí <sean@example.com>".to_string(),
-         ) );
+        let to = To::from(Mailboxes::from_iter([
+            "🌍 <world@example.com>".parse().unwrap(),
+            "🦆 Everywhere <ducks@example.com>".parse().unwrap(),
+            "Иванов Иван Иванович <ivanov@example.com>".parse().unwrap(),
+            "Jānis Bērziņš <janis@example.com>".parse().unwrap(),
+            "Seán Ó Rudaí <sean@example.com>".parse().unwrap(),
+        ]));
+        headers.set(to);
 
         assert_eq!(
             headers.to_string(),
             concat!(
-                "To: =?utf-8?b?8J+MjQ==?= <world@example.com>, =?utf-8?b?8J+mhg==?= \r\n",
-                " Everywhere <ducks@example.com>, =?utf-8?b?0JjQstCw0L3QvtCyIA==?=\r\n",
-                " =?utf-8?b?0JjQstCw0L0g0JjQstCw0L3QvtCy0LjRhw==?= <ivanov@example.com>, \r\n",
-                " =?utf-8?b?SsSBbmlzIELEk3J6acWGxaE=?= <janis@example.com>, \r\n",
-                " =?utf-8?b?U2XDoW4gw5MgUnVkYcOt?= <sean@example.com>\r\n"
+                "To: =?utf-8?b?8J+MjQ==?= <world@example.com>, =?utf-8?b?8J+mhiBFdmVyeXdo?=\r\n",
+                " =?utf-8?b?ZXJl?= <ducks@example.com>, =?utf-8?b?0JjQstCw0L3QvtCyINCY0LI=?=\r\n",
+                " =?utf-8?b?0LDQvSDQmNCy0LDQvdC+0LLQuNGH?= <ivanov@example.com>,\r\n",
+                " =?utf-8?b?SsSBbmlzIELEk3J6acWGxaE=?= <janis@example.com>, =?utf-8?b?U2U=?=\r\n",
+                " =?utf-8?b?w6FuIMOTIFJ1ZGHDrQ==?= <sean@example.com>\r\n",
+            )
+        );
+    }
+
+    #[test]
+    fn format_special_with_folding_raw() {
+        let mut headers = Headers::new();
+        headers.insert_raw(HeaderValue::new(
+            HeaderName::new_from_ascii_str("To"),
+            "🌍 <world@example.com>, 🦆 Everywhere <ducks@example.com>, Иванов Иван Иванович <ivanov@example.com>, Jānis Bērziņš <janis@example.com>, Seán Ó Rudaí <sean@example.com>".to_owned(),
+        ));
+
+        // TODO: fix the fact that the encoder doesn't know that
+        // the space between the name and the address should be
+        // removed when wrapping.
+        assert_eq!(
+            headers.to_string(),
+            concat!(
+                "To: =?utf-8?b?8J+MjQ==?= <world@example.com>, =?utf-8?b?8J+mhg==?=\r\n",
+                " Everywhere <ducks@example.com>, =?utf-8?b?0JjQstCw0L3QvtCyINCY0LLQsNC9?=\r\n",
+                " =?utf-8?b?INCY0LLQsNC90L7QstC40Yc=?= <ivanov@example.com>,\r\n",
+                "  =?utf-8?b?SsSBbmlzIELEk3J6acWGxaE=?= <janis@example.com>,\r\n",
+                "  =?utf-8?b?U2XDoW4gw5MgUnVkYcOt?= <sean@example.com>\r\n",
             )
         );
     }
@@ -759,12 +633,19 @@ mod tests {
         headers.insert_raw(
             HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳".to_string(),)
+            "🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳".to_owned(),)
         );
 
         assert_eq!(
             headers.to_string(),
-            "Subject: =?utf-8?b?8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz?=\r\n"
+            concat!(
+                "Subject: =?utf-8?b?8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz?=\r\n",
+                " =?utf-8?b?8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbM=?=\r\n",
+                " =?utf-8?b?8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbM=?=\r\n",
+                " =?utf-8?b?8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbM=?=\r\n",
+                " =?utf-8?b?8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+ls/CfpbM=?=\r\n",
+                " =?utf-8?b?8J+ls/CfpbPwn6Wz8J+ls/CfpbPwn6Wz8J+lsw==?=\r\n"
+            )
         );
     }
 
@@ -773,7 +654,7 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "Hello! \r\n This is \" bad \0. 👋".to_string(),
+            "Hello! \r\n This is \" bad \0. 👋".to_owned(),
         ));
 
         assert_eq!(
@@ -788,35 +669,38 @@ mod tests {
         headers.insert_raw(
             HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "Hello! This is lettre, and this IsAVeryLongLineDoYouKnowWhatsGoingToHappenIGuessWeAreGoingToFindOut. Ok I guess that's it!".to_string()
+            "Hello! This is lettre, and this IsAVeryLongLineDoYouKnowWhatsGoingToHappenIGuessWeAreGoingToFindOut. Ok I guess that's it!".to_owned()
             )
         );
         headers.insert_raw(
             HeaderValue::new(
             HeaderName::new_from_ascii_str("To"),
-            "🌍 <world@example.com>, 🦆 Everywhere <ducks@example.com>, Иванов Иван Иванович <ivanov@example.com>, Jānis Bērziņš <janis@example.com>, Seán Ó Rudaí <sean@example.com>".to_string(),
+            "🌍 <world@example.com>, 🦆 Everywhere <ducks@example.com>, Иванов Иван Иванович <ivanov@example.com>, Jānis Bērziņš <janis@example.com>, Seán Ó Rudaí <sean@example.com>".to_owned(),
             )
         );
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("From"),
-            "Someone <somewhere@example.com>".to_string(),
+            "Someone <somewhere@example.com>".to_owned(),
         ));
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Transfer-Encoding"),
-            "quoted-printable".to_string(),
+            "quoted-printable".to_owned(),
         ));
 
+        // TODO: fix the fact that the encoder doesn't know that
+        // the space between the name and the address should be
+        // removed when wrapping.
         assert_eq!(
             headers.to_string(),
             concat!(
-                "Subject: Hello! This is lettre, and this \r\n",
-                " IsAVeryLongLineDoYouKnowWhatsGoingToHappenIGuessWeAreGoingToFindOut. Ok I \r\n",
+                "Subject: Hello! This is lettre, and this\r\n",
+                " IsAVeryLongLineDoYouKnowWhatsGoingToHappenIGuessWeAreGoingToFindOut. Ok I\r\n",
                 " guess that's it!\r\n",
-                "To: =?utf-8?b?8J+MjQ==?= <world@example.com>, =?utf-8?b?8J+mhg==?= \r\n",
-                " Everywhere <ducks@example.com>, =?utf-8?b?0JjQstCw0L3QvtCyIA==?=\r\n",
-                " =?utf-8?b?0JjQstCw0L0g0JjQstCw0L3QvtCy0LjRhw==?= <ivanov@example.com>, \r\n",
-                " =?utf-8?b?SsSBbmlzIELEk3J6acWGxaE=?= <janis@example.com>, \r\n",
-                " =?utf-8?b?U2XDoW4gw5MgUnVkYcOt?= <sean@example.com>\r\n",
+                "To: =?utf-8?b?8J+MjQ==?= <world@example.com>, =?utf-8?b?8J+mhg==?=\r\n",
+                " Everywhere <ducks@example.com>, =?utf-8?b?0JjQstCw0L3QvtCyINCY0LLQsNC9?=\r\n",
+                " =?utf-8?b?INCY0LLQsNC90L7QstC40Yc=?= <ivanov@example.com>,\r\n",
+                "  =?utf-8?b?SsSBbmlzIELEk3J6acWGxaE=?= <janis@example.com>,\r\n",
+                "  =?utf-8?b?U2XDoW4gw5MgUnVkYcOt?= <sean@example.com>\r\n",
                 "From: Someone <somewhere@example.com>\r\n",
                 "Content-Transfer-Encoding: quoted-printable\r\n",
             )
@@ -828,14 +712,14 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "＋仮名 :a;go; ;;;;;s;;;;;;;;;;;;;;;;fffeinmjgggggggggｆっ".to_string(),
+            "＋仮名 :a;go; ;;;;;s;;;;;;;;;;;;;;;;fffeinmjgggggggggｆっ".to_owned(),
         ));
 
         assert_eq!(
             headers.to_string(),
             concat!(
-                "Subject: =?utf-8?b?77yL5Luu5ZCN?= :a;go; \r\n",
-                " =?utf-8?b?Ozs7OztzOzs7Ozs7Ozs7Ozs7Ozs7O2ZmZmVpbm1qZ2dnZ2dnZ2dn772G44Gj?=\r\n"
+                "Subject: =?utf-8?b?77yL5Luu5ZCN?= :a;go; =?utf-8?b?Ozs7OztzOzs7Ozs7Ozs7?=\r\n",
+                " =?utf-8?b?Ozs7Ozs7O2ZmZmVpbm1qZ2dnZ2dnZ2dn772G44Gj?=\r\n",
             )
         );
     }

src/message/header/special.rs

@@ -4,7 +4,7 @@ use crate::{
 };
 
 /// Message format version, defined in [RFC2045](https://tools.ietf.org/html/rfc2045#section-4)
-#[derive(Debug, Copy, Clone, PartialEq)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub struct MimeVersion {
     major: u8,
     minor: u8,
@@ -16,15 +16,18 @@ pub struct MimeVersion {
 pub const MIME_VERSION_1_0: MimeVersion = MimeVersion::new(1, 0);
 
 impl MimeVersion {
+    /// Build a new `MimeVersion` header
     pub const fn new(major: u8, minor: u8) -> Self {
         MimeVersion { major, minor }
     }
 
+    /// Get the `major` value of this `MimeVersion` header.
     #[inline]
     pub const fn major(self) -> u8 {
         self.major
     }
 
+    /// Get the `minor` value of this `MimeVersion` header.
     #[inline]
     pub const fn minor(self) -> u8 {
         self.minor
@@ -64,6 +67,8 @@ impl Default for MimeVersion {
 
 #[cfg(test)]
 mod test {
+    use pretty_assertions::assert_eq;
+
     use super::{MimeVersion, MIME_VERSION_1_0};
     use crate::message::header::{HeaderName, HeaderValue, Headers};
 
@@ -86,14 +91,14 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("MIME-Version"),
-            "1.0".to_string(),
+            "1.0".to_owned(),
         ));
 
         assert_eq!(headers.get::<MimeVersion>(), Some(MIME_VERSION_1_0));
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("MIME-Version"),
-            "0.1".to_string(),
+            "0.1".to_owned(),
         ));
 
         assert_eq!(headers.get::<MimeVersion>(), Some(MimeVersion::new(0, 1)));

src/message/header/textual.rs

@@ -4,7 +4,7 @@ use crate::BoxError;
 macro_rules! text_header {
     ($(#[$attr:meta])* Header($type_name: ident, $header_name: expr )) => {
         $(#[$attr])*
-        #[derive(Debug, Clone, PartialEq)]
+        #[derive(Debug, Clone, PartialEq, Eq)]
         pub struct $type_name(String);
 
         impl Header for $type_name {
@@ -85,6 +85,8 @@ text_header! {
 
 #[cfg(test)]
 mod test {
+    use pretty_assertions::assert_eq;
+
     use super::Subject;
     use crate::message::header::{HeaderName, HeaderValue, Headers};
 
@@ -107,12 +109,23 @@ mod test {
         );
     }
 
+    #[test]
+    fn format_utf8_word() {
+        let mut headers = Headers::new();
+        headers.set(Subject("Administratör".into()));
+
+        assert_eq!(
+            headers.to_string(),
+            "Subject: =?utf-8?b?QWRtaW5pc3RyYXTDtnI=?=\r\n"
+        );
+    }
+
     #[test]
     fn parse_ascii() {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "Sample subject".to_string(),
+            "Sample subject".to_owned(),
         ));
 
         assert_eq!(

src/message/mailbox/mod.rs

@@ -1,3 +1,4 @@
+mod parsers;
 #[cfg(feature = "serde")]
 mod serde;
 mod types;

src/message/mailbox/parsers/mod.rs

@@ -0,0 +1,5 @@
+mod rfc2234;
+mod rfc2822;
+mod rfc5336;
+
+pub(crate) use rfc2822::{mailbox, mailbox_list};

src/message/mailbox/parsers/rfc2234.rs

@@ -0,0 +1,32 @@
+//! Partial parsers implementation of [RFC2234]: Augmented BNF for
+//! Syntax Specifications: ABNF.
+//!
+//! [RFC2234]: https://datatracker.ietf.org/doc/html/rfc2234
+
+use chumsky::{error::Cheap, prelude::*};
+
+// 6.1  Core Rules
+// https://datatracker.ietf.org/doc/html/rfc2234#section-6.1
+
+// ALPHA          =  %x41-5A / %x61-7A   ; A-Z / a-z
+pub(super) fn alpha() -> impl Parser<char, char, Error = Cheap<char>> {
+    filter(|c: &char| c.is_ascii_alphabetic())
+}
+
+// DIGIT          =  %x30-39
+//                        ; 0-9
+pub(super) fn digit() -> impl Parser<char, char, Error = Cheap<char>> {
+    filter(|c: &char| c.is_ascii_digit())
+}
+
+// DQUOTE         =  %x22
+//                        ; " (Double Quote)
+pub(super) fn dquote() -> impl Parser<char, char, Error = Cheap<char>> {
+    just('"')
+}
+
+// WSP            =  SP / HTAB
+//                        ; white space
+pub(super) fn wsp() -> impl Parser<char, char, Error = Cheap<char>> {
+    choice((just(' '), just('\t')))
+}

src/message/mailbox/parsers/rfc2822.rs

@@ -0,0 +1,248 @@
+//! Partial parsers implementation of [RFC2822]: Internet Message
+//! Format.
+//!
+//! [RFC2822]: https://datatracker.ietf.org/doc/html/rfc2822
+
+use chumsky::{error::Cheap, prelude::*};
+
+use super::{rfc2234, rfc5336};
+
+// 3.2.1. Primitive Tokens
+// https://datatracker.ietf.org/doc/html/rfc2822#section-3.2.1
+
+// NO-WS-CTL       =       %d1-8 /         ; US-ASCII control characters
+//                         %d11 /          ;  that do not include the
+//                         %d12 /          ;  carriage return, line feed,
+//                         %d14-31 /       ;  and white space characters
+//                         %d127
+fn no_ws_ctl() -> impl Parser<char, char, Error = Cheap<char>> {
+    filter(|c| matches!(u32::from(*c), 1..=8 | 11 | 12 | 14..=31 | 127))
+}
+
+// text            =       %d1-9 /         ; Characters excluding CR and LF
+//                         %d11 /
+//                         %d12 /
+//                         %d14-127 /
+//                         obs-text
+fn text() -> impl Parser<char, char, Error = Cheap<char>> {
+    filter(|c| matches!(u32::from(*c), 1..=9 | 11 | 12 | 14..=127))
+}
+
+// 3.2.2. Quoted characters
+// https://datatracker.ietf.org/doc/html/rfc2822#section-3.2.2
+
+// quoted-pair     =       ("\" text) / obs-qp
+fn quoted_pair() -> impl Parser<char, char, Error = Cheap<char>> {
+    just('\\').ignore_then(text())
+}
+
+// 3.2.3. Folding white space and comments
+// https://datatracker.ietf.org/doc/html/rfc2822#section-3.2.3
+
+// FWS             =       ([*WSP CRLF] 1*WSP) /   ; Folding white space
+//                         obs-FWS
+pub fn fws() -> impl Parser<char, Option<char>, Error = Cheap<char>> {
+    rfc2234::wsp()
+        .or_not()
+        .then_ignore(rfc2234::wsp().ignored().repeated())
+}
+
+// CFWS            =       *([FWS] comment) (([FWS] comment) / FWS)
+pub fn cfws() -> impl Parser<char, Option<char>, Error = Cheap<char>> {
+    // TODO: comment are not currently supported, so for now a cfws is
+    // the same as a fws.
+    fws()
+}
+
+// 3.2.4. Atom
+// https://datatracker.ietf.org/doc/html/rfc2822#section-3.2.4
+
+// atext           =       ALPHA / DIGIT / ; Any character except controls,
+//                         "!" / "#" /     ;  SP, and specials.
+//                         "$" / "%" /     ;  Used for atoms
+//                         "&" / "'" /
+//                         "*" / "+" /
+//                         "-" / "/" /
+//                         "=" / "?" /
+//                         "^" / "_" /
+//                         "`" / "{" /
+//                         "|" / "}" /
+//                         "~"
+pub(super) fn atext() -> impl Parser<char, char, Error = Cheap<char>> {
+    choice((
+        rfc2234::alpha(),
+        rfc2234::digit(),
+        filter(|c| {
+            matches!(
+                *c,
+                '!' | '#'
+                    | '$'
+                    | '%'
+                    | '&'
+                    | '\''
+                    | '*'
+                    | '+'
+                    | '-'
+                    | '/'
+                    | '='
+                    | '?'
+                    | '^'
+                    | '_'
+                    | '`'
+                    | '{'
+                    | '|'
+                    | '}'
+                    | '~'
+            )
+        }),
+        // also allow non ASCII UTF8 chars
+        rfc5336::utf8_non_ascii(),
+    ))
+}
+
+// atom            =       [CFWS] 1*atext [CFWS]
+pub(super) fn atom() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+    cfws().chain(atext().repeated().at_least(1))
+}
+
+// dot-atom        =       [CFWS] dot-atom-text [CFWS]
+pub fn dot_atom() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+    cfws().chain(dot_atom_text())
+}
+
+// dot-atom-text   =       1*atext *("." 1*atext)
+pub fn dot_atom_text() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+    atext().repeated().at_least(1).chain(
+        just('.')
+            .chain(atext().repeated().at_least(1))
+            .repeated()
+            .at_least(1)
+            .flatten(),
+    )
+}
+
+// 3.2.5. Quoted strings
+// https://datatracker.ietf.org/doc/html/rfc2822#section-3.2.5
+
+// qtext           =       NO-WS-CTL /     ; Non white space controls
+//
+//                         %d33 /          ; The rest of the US-ASCII
+//                         %d35-91 /       ;  characters not including "\"
+//                         %d93-126        ;  or the quote character
+fn qtext() -> impl Parser<char, char, Error = Cheap<char>> {
+    choice((
+        filter(|c| matches!(u32::from(*c), 33 | 35..=91 | 93..=126)),
+        no_ws_ctl(),
+    ))
+}
+
+// qcontent        =       qtext / quoted-pair
+pub(super) fn qcontent() -> impl Parser<char, char, Error = Cheap<char>> {
+    choice((qtext(), quoted_pair(), rfc5336::utf8_non_ascii()))
+}
+
+// quoted-string   =       [CFWS]
+//                         DQUOTE *([FWS] qcontent) [FWS] DQUOTE
+//                         [CFWS]
+fn quoted_string() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+    rfc2234::dquote()
+        .ignore_then(fws().chain(qcontent()).repeated().flatten())
+        .then_ignore(text::whitespace())
+        .then_ignore(rfc2234::dquote())
+}
+
+// 3.2.6. Miscellaneous tokens
+// https://datatracker.ietf.org/doc/html/rfc2822#section-3.2.6
+
+// word            =       atom / quoted-string
+fn word() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+    choice((quoted_string(), atom()))
+}
+
+// phrase          =       1*word / obs-phrase
+fn phrase() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+    choice((obs_phrase(), word().repeated().at_least(1).flatten()))
+}
+
+// 3.4. Address Specification
+// https://datatracker.ietf.org/doc/html/rfc2822#section-3.4
+
+// mailbox         =       name-addr / addr-spec
+pub(crate) fn mailbox() -> impl Parser<char, (Option<String>, (String, String)), Error = Cheap<char>>
+{
+    choice((name_addr(), addr_spec().map(|addr| (None, addr)))).then_ignore(end())
+}
+
+// name-addr       =       [display-name] angle-addr
+fn name_addr() -> impl Parser<char, (Option<String>, (String, String)), Error = Cheap<char>> {
+    display_name().collect().or_not().then(angle_addr())
+}
+
+// angle-addr      =       [CFWS] "<" addr-spec ">" [CFWS] / obs-angle-addr
+fn angle_addr() -> impl Parser<char, (String, String), Error = Cheap<char>> {
+    addr_spec()
+        .delimited_by(just('<').ignored(), just('>').ignored())
+        .padded()
+}
+
+// display-name    =       phrase
+fn display_name() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+    phrase()
+}
+
+// mailbox-list    =       (mailbox *("," mailbox)) / obs-mbox-list
+pub(crate) fn mailbox_list(
+) -> impl Parser<char, Vec<(Option<String>, (String, String))>, Error = Cheap<char>> {
+    choice((name_addr(), addr_spec().map(|addr| (None, addr))))
+        .separated_by(just(',').padded())
+        .then_ignore(end())
+}
+
+// 3.4.1. Addr-spec specification
+// https://datatracker.ietf.org/doc/html/rfc2822#section-3.4.1
+
+// addr-spec       =       local-part "@" domain
+pub fn addr_spec() -> impl Parser<char, (String, String), Error = Cheap<char>> {
+    local_part()
+        .collect()
+        .then_ignore(just('@'))
+        .then(domain().collect())
+}
+
+// local-part      =       dot-atom / quoted-string / obs-local-part
+pub fn local_part() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+    choice((dot_atom(), quoted_string(), obs_local_part()))
+}
+
+// domain          =       dot-atom / domain-literal / obs-domain
+pub fn domain() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+    // NOTE: omitting domain-literal since it may never be used
+    choice((dot_atom(), obs_domain()))
+}
+
+// 4.1. Miscellaneous obsolete tokens
+// https://datatracker.ietf.org/doc/html/rfc2822#section-4.1
+
+// obs-phrase      =       word *(word / "." / CFWS)
+fn obs_phrase() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+    // NOTE: the CFWS is already captured by the word, no need to add
+    // it there.
+    word().chain(
+        choice((word(), just('.').repeated().exactly(1)))
+            .repeated()
+            .flatten(),
+    )
+}
+
+// 4.4. Obsolete Addressing
+// https://datatracker.ietf.org/doc/html/rfc2822#section-4.4
+
+// obs-local-part  =       word *("." word)
+pub fn obs_local_part() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+    word().chain(just('.').chain(word()).repeated().flatten())
+}
+
+// obs-domain      =       atom *("." atom)
+pub fn obs_domain() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+    atom().chain(just('.').chain(atom()).repeated().flatten())
+}

src/message/mailbox/parsers/rfc5336.rs

@@ -0,0 +1,17 @@
+//! Partial parsers implementation of [RFC5336]: SMTP Extension for
+//! Internationalized Email Addresses.
+//!
+//! [RFC5336]: https://datatracker.ietf.org/doc/html/rfc5336
+
+use chumsky::{error::Cheap, prelude::*};
+
+// 3.3.  Extended Mailbox Address Syntax
+// https://datatracker.ietf.org/doc/html/rfc5336#section-3.3
+
+// UTF8-non-ascii = UTF8-2 / UTF8-3 / UTF8-4
+// UTF8-2 =  <See Section 4 of RFC 3629>
+// UTF8-3 =  <See Section 4 of RFC 3629>
+// UTF8-4 =  <See Section 4 of RFC 3629>
+pub(super) fn utf8_non_ascii() -> impl Parser<char, char, Error = Cheap<char>> {
+    filter(|c: &char| c.len_utf8() > 1)
+}

src/message/mailbox/serde.rs

@@ -13,7 +13,7 @@ impl Serialize for Mailbox {
     where
         S: Serializer,
     {
-        serializer.serialize_str(&self.to_string())
+        serializer.collect_str(self)
     }
 }
 
@@ -111,7 +111,7 @@ impl Serialize for Mailboxes {
     where
         S: Serializer,
     {
-        serializer.serialize_str(&self.to_string())
+        serializer.collect_str(self)
     }
 }
 
@@ -154,6 +154,7 @@ impl<'de> Deserialize<'de> for Mailboxes {
 
 #[cfg(test)]
 mod test {
+    use pretty_assertions::assert_eq;
     use serde_json::from_str;
 
     use super::*;
@@ -178,7 +179,7 @@ mod test {
     }
 
     #[test]
-    fn parse_mailbox_object_address_stirng() {
+    fn parse_mailbox_object_address_string() {
         let m: Mailbox = from_str(r#"{ "name": "Kai", "email": "kayo@example.com" }"#).unwrap();
         assert_eq!(m, "Kai <kayo@example.com>".parse().unwrap());
     }
@@ -197,7 +198,7 @@ mod test {
             from_str(r#""yin@dtb.com, Hei <hei@dtb.com>, Kai <kayo@example.com>""#).unwrap();
         assert_eq!(
             m,
-            "<yin@dtb.com>, Hei <hei@dtb.com>, Kai <kayo@example.com>"
+            "yin@dtb.com, Hei <hei@dtb.com>, Kai <kayo@example.com>"
                 .parse()
                 .unwrap()
         );
@@ -210,7 +211,7 @@ mod test {
                 .unwrap();
         assert_eq!(
             m,
-            "<yin@dtb.com>, Hei <hei@dtb.com>, Kai <kayo@example.com>"
+            "yin@dtb.com, Hei <hei@dtb.com>, Kai <kayo@example.com>"
                 .parse()
                 .unwrap()
         );

src/message/mailbox/types.rs

@@ -5,15 +5,17 @@ use std::{
     str::FromStr,
 };
 
+use chumsky::prelude::*;
 use email_encoding::headers::EmailWriter;
 
+use super::parsers;
 use crate::address::{Address, AddressError};
 
 /// Represents an email address with an optional name for the sender/recipient.
 ///
 /// This type contains email address and the sender/recipient name (_Some Name \<user@domain.tld\>_ or _withoutname@domain.tld_).
 ///
-/// **NOTE**: Enable feature "serde" to be able serialize/deserialize it using [serde](https://serde.rs/).
+/// **NOTE**: Enable feature "serde" to be able to serialize/deserialize it using [serde](https://serde.rs/).
 ///
 /// # Examples
 ///
@@ -70,7 +72,7 @@ impl Mailbox {
     pub(crate) fn encode(&self, w: &mut EmailWriter<'_>) -> FmtResult {
         if let Some(name) = &self.name {
             email_encoding::headers::quoted_string::encode(name, w)?;
-            w.space();
+            w.optional_breakpoint();
             w.write_char('<')?;
         }
 
@@ -86,7 +88,7 @@ impl Mailbox {
 
 impl Display for Mailbox {
     fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
-        if let Some(ref name) = self.name {
+        if let Some(name) = &self.name {
             let name = name.trim();
             if !name.is_empty() {
                 write_word(f, name)?;
@@ -108,40 +110,24 @@ impl<S: Into<String>, T: Into<String>> TryFrom<(S, T)> for Mailbox {
     }
 }
 
-/*
-impl<S: AsRef<&str>, T: AsRef<&str>> TryFrom<(S, T)> for Mailbox {
-    type Error = AddressError;
-
-    fn try_from(header: (S, T)) -> Result<Self, Self::Error> {
-        let (name, address) = header;
-        Ok(Mailbox::new(Some(name.as_ref()), address.as_ref().parse()?))
-    }
-}*/
-
 impl FromStr for Mailbox {
     type Err = AddressError;
 
     fn from_str(src: &str) -> Result<Mailbox, Self::Err> {
-        match (src.find('<'), src.find('>')) {
-            (Some(addr_open), Some(addr_close)) if addr_open < addr_close => {
-                let name = src.split_at(addr_open).0;
-                let addr_open = addr_open + 1;
-                let addr = src.split_at(addr_open).1.split_at(addr_close - addr_open).0;
-                let addr = addr.parse()?;
-                let name = name.trim();
-                let name = if name.is_empty() {
-                    None
-                } else {
-                    Some(name.into())
-                };
-                Ok(Mailbox::new(name, addr))
-            }
-            (Some(_), _) => Err(AddressError::Unbalanced),
-            _ => {
-                let addr = src.parse()?;
-                Ok(Mailbox::new(None, addr))
-            }
-        }
+        let (name, (user, domain)) = parsers::mailbox().parse(src).map_err(|_errs| {
+            // TODO: improve error management
+            AddressError::InvalidInput
+        })?;
+
+        let mailbox = Mailbox::new(name, Address::new(user, domain)?);
+
+        Ok(mailbox)
+    }
+}
+
+impl From<Address> for Mailbox {
+    fn from(value: Address) -> Self {
+        Self::new(None, value)
     }
 }
 
@@ -149,7 +135,7 @@ impl FromStr for Mailbox {
 ///
 /// This type contains a sequence of mailboxes (_Some Name \<user@domain.tld\>, Another Name \<other@domain.tld\>, withoutname@domain.tld, ..._).
 ///
-/// **NOTE**: Enable feature "serde" to be able serialize/deserialize it using [serde](https://serde.rs/).
+/// **NOTE**: Enable feature "serde" to be able to serialize/deserialize it using [serde](https://serde.rs/).
 #[derive(Debug, Clone, PartialOrd, Ord, PartialEq, Eq, Hash)]
 pub struct Mailboxes(Vec<Mailbox>);
 
@@ -275,7 +261,7 @@ impl Mailboxes {
         for mailbox in self.iter() {
             if !mem::take(&mut first) {
                 w.write_char(',')?;
-                w.space();
+                w.optional_breakpoint();
             }
 
             mailbox.encode(w)?;
@@ -315,6 +301,18 @@ impl From<Mailboxes> for Vec<Mailbox> {
     }
 }
 
+impl FromIterator<Mailbox> for Mailboxes {
+    fn from_iter<T: IntoIterator<Item = Mailbox>>(iter: T) -> Self {
+        Self(Vec::from_iter(iter))
+    }
+}
+
+impl Extend<Mailbox> for Mailboxes {
+    fn extend<T: IntoIterator<Item = Mailbox>>(&mut self, iter: T) {
+        self.0.extend(iter);
+    }
+}
+
 impl IntoIterator for Mailboxes {
     type Item = Mailbox;
     type IntoIter = ::std::vec::IntoIter<Mailbox>;
@@ -324,14 +322,6 @@ impl IntoIterator for Mailboxes {
     }
 }
 
-impl Extend<Mailbox> for Mailboxes {
-    fn extend<T: IntoIterator<Item = Mailbox>>(&mut self, iter: T) {
-        for elem in iter {
-            self.0.push(elem);
-        }
-    }
-}
-
 impl Display for Mailboxes {
     fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
         let mut iter = self.iter();
@@ -352,34 +342,16 @@ impl Display for Mailboxes {
 impl FromStr for Mailboxes {
     type Err = AddressError;
 
-    fn from_str(mut src: &str) -> Result<Self, Self::Err> {
+    fn from_str(src: &str) -> Result<Self, Self::Err> {
         let mut mailboxes = Vec::new();
 
-        if !src.is_empty() {
-            // n-1 elements
-            let mut skip = 0;
-            while let Some(i) = src[skip..].find(',') {
-                let left = &src[..skip + i];
+        let parsed_mailboxes = parsers::mailbox_list().parse(src).map_err(|_errs| {
+            // TODO: improve error management
+            AddressError::InvalidInput
+        })?;
 
-                match left.trim().parse() {
-                    Ok(mailbox) => {
-                        mailboxes.push(mailbox);
-
-                        src = &src[left.len() + ",".len()..];
-                        skip = 0;
-                    }
-                    Err(AddressError::MissingParts) => {
-                        skip = left.len() + ",".len();
-                    }
-                    Err(err) => {
-                        return Err(err);
-                    }
-                }
-            }
-
-            // last element
-            let mailbox = src.trim().parse()?;
-            mailboxes.push(mailbox);
+        for (name, (user, domain)) in parsed_mailboxes {
+            mailboxes.push(Mailbox::new(name, Address::new(user, domain)?))
         }
 
         Ok(Mailboxes(mailboxes))
@@ -393,7 +365,7 @@ fn write_word(f: &mut Formatter<'_>, s: &str) -> FmtResult {
     } else {
         // Quoted string: https://datatracker.ietf.org/doc/html/rfc2822#section-3.2.5
         f.write_char('"')?;
-        for &c in s.as_bytes() {
+        for c in s.chars() {
             write_quoted_string_char(f, c)?;
         }
         f.write_char('"')?;
@@ -432,45 +404,50 @@ fn is_valid_atom_char(c: u8) -> bool {
 		b'}' |
 		b'~' |
 
-		// Not techically allowed but will be escaped into allowed characters.
+		// Not technically allowed but will be escaped into allowed characters.
 		128..=255)
 }
 
 // https://datatracker.ietf.org/doc/html/rfc2822#section-3.2.5
-fn write_quoted_string_char(f: &mut Formatter<'_>, c: u8) -> FmtResult {
+fn write_quoted_string_char(f: &mut Formatter<'_>, c: char) -> FmtResult {
     match c {
-		// NO-WS-CTL: https://datatracker.ietf.org/doc/html/rfc2822#section-3.2.1
-		1..=8 | 11 | 12 | 14..=31 | 127 |
+        // Can not be encoded.
+        '\n' | '\r' => Err(std::fmt::Error),
 
-		// Note, not qcontent but can be put before or after any qcontent.
-		b'\t' |
-		b' ' |
+        // Note, not qcontent but can be put before or after any qcontent.
+        '\t' | ' ' => f.write_char(c),
 
-		// The rest of the US-ASCII except \ and "
-		33 |
-		35..=91 |
-		93..=126 |
+        c if match c as u32 {
+            // NO-WS-CTL: https://datatracker.ietf.org/doc/html/rfc2822#section-3.2.1
+            1..=8 | 11 | 12 | 14..=31 | 127 |
 
-		// Non-ascii characters will be escaped separately later.
-		128..=255
+            // The rest of the US-ASCII except \ and "
+            33 |
+            35..=91 |
+            93..=126 |
 
-		=> f.write_char(c.into()),
+            // Non-ascii characters will be escaped separately later.
+            128.. => true,
+            _ => false,
+        } =>
+        {
+            f.write_char(c)
+        }
 
-		// Can not be encoded.
-		b'\n' | b'\r' => Err(std::fmt::Error),
-
-		c => {
-			// quoted-pair https://datatracker.ietf.org/doc/html/rfc2822#section-3.2.2
-			f.write_char('\\')?;
-			f.write_char(c.into())
-		}
-	}
+        _ => {
+            // quoted-pair https://datatracker.ietf.org/doc/html/rfc2822#section-3.2.2
+            f.write_char('\\')?;
+            f.write_char(c)
+        }
+    }
 }
 
 #[cfg(test)]
 mod test {
     use std::convert::TryInto;
 
+    use pretty_assertions::assert_eq;
+
     use super::Mailbox;
 
     #[test]
@@ -509,6 +486,34 @@ mod test {
         );
     }
 
+    #[test]
+    fn mailbox_format_address_with_comma_and_non_ascii() {
+        assert_eq!(
+            format!(
+                "{}",
+                Mailbox::new(
+                    Some("Laşt, First".into()),
+                    "kayo@example.com".parse().unwrap()
+                )
+            ),
+            r#""Laşt, First" <kayo@example.com>"#
+        );
+    }
+
+    #[test]
+    fn mailbox_format_address_with_comma_and_quoted_non_ascii() {
+        assert_eq!(
+            format!(
+                "{}",
+                Mailbox::new(
+                    Some(r#"Laşt, "First""#.into()),
+                    "kayo@example.com".parse().unwrap()
+                )
+            ),
+            r#""Laşt, \"First\"" <kayo@example.com>"#
+        );
+    }
+
     #[test]
     fn mailbox_format_address_with_color() {
         assert_eq!(
@@ -583,7 +588,7 @@ mod test {
     #[test]
     fn parse_address_from_tuple() {
         assert_eq!(
-            ("K.".to_string(), "kayo@example.com".to_string()).try_into(),
+            ("K.".to_owned(), "kayo@example.com".to_owned()).try_into(),
             Ok(Mailbox::new(
                 Some("K.".into()),
                 "kayo@example.com".parse().unwrap()

src/message/mimebody.rs

@@ -17,6 +17,16 @@ pub(super) enum Part {
     Multi(MultiPart),
 }
 
+impl Part {
+    #[cfg(feature = "dkim")]
+    pub(super) fn format_body(&self, out: &mut Vec<u8>) {
+        match self {
+            Part::Single(part) => part.format_body(out),
+            Part::Multi(part) => part.format_body(out),
+        }
+    }
+}
+
 impl EmailFormat for Part {
     fn format(&self, out: &mut Vec<u8>) {
         match self {
@@ -100,14 +110,14 @@ impl SinglePart {
         SinglePartBuilder::new()
     }
 
-    /// Directly create a `SinglePart` from an plain UTF-8 content
+    /// Directly create a `SinglePart` from a plain UTF-8 content
     pub fn plain<T: IntoBody>(body: T) -> Self {
         Self::builder()
             .header(header::ContentType::TEXT_PLAIN)
             .body(body)
     }
 
-    /// Directly create a `SinglePart` from an UTF-8 HTML content
+    /// Directly create a `SinglePart` from a UTF-8 HTML content
     pub fn html<T: IntoBody>(body: T) -> Self {
         Self::builder()
             .header(header::ContentType::TEXT_HTML)
@@ -132,6 +142,12 @@ impl SinglePart {
         self.format(&mut out);
         out
     }
+
+    /// Format only the signlepart body
+    fn format_body(&self, out: &mut Vec<u8>) {
+        out.extend_from_slice(&self.body);
+        out.extend_from_slice(b"\r\n");
+    }
 }
 
 impl EmailFormat for SinglePart {
@@ -139,8 +155,7 @@ impl EmailFormat for SinglePart {
         write!(out, "{}", self.headers)
             .expect("A Write implementation panicked while formatting headers");
         out.extend_from_slice(b"\r\n");
-        out.extend_from_slice(&self.body);
-        out.extend_from_slice(b"\r\n");
+        self.format_body(out);
     }
 }
 
@@ -149,17 +164,17 @@ impl EmailFormat for SinglePart {
 pub enum MultiPartKind {
     /// Mixed kind to combine unrelated content parts
     ///
-    /// For example this kind can be used to mix email message and attachments.
+    /// For example, this kind can be used to mix an email message and attachments.
     Mixed,
 
     /// Alternative kind to join several variants of same email contents.
     ///
-    /// That kind is recommended to use for joining plain (text) and rich (HTML) messages into single email message.
+    /// That kind is recommended to use for joining plain (text) and rich (HTML) messages into a single email message.
     Alternative,
 
     /// Related kind to mix content and related resources.
     ///
-    /// For example, you can include images into HTML content using that.
+    /// For example, you can include images in HTML content using that.
     Related,
 
     /// Encrypted kind for encrypted messages
@@ -190,9 +205,9 @@ impl MultiPartKind {
             },
             boundary,
             match self {
-                Self::Encrypted { protocol } => format!("; protocol=\"{}\"", protocol),
+                Self::Encrypted { protocol } => format!("; protocol=\"{protocol}\""),
                 Self::Signed { protocol, micalg } =>
-                    format!("; protocol=\"{}\"; micalg=\"{}\"", protocol, micalg),
+                    format!("; protocol=\"{protocol}\"; micalg=\"{micalg}\""),
                 _ => String::new(),
             }
         )
@@ -373,14 +388,9 @@ impl MultiPart {
         self.format(&mut out);
         out
     }
-}
-
-impl EmailFormat for MultiPart {
-    fn format(&self, out: &mut Vec<u8>) {
-        write!(out, "{}", self.headers)
-            .expect("A Write implementation panicked while formatting headers");
-        out.extend_from_slice(b"\r\n");
 
+    /// Format only the multipart body
+    fn format_body(&self, out: &mut Vec<u8>) {
         let boundary = self.boundary();
 
         for part in &self.parts {
@@ -396,8 +406,19 @@ impl EmailFormat for MultiPart {
     }
 }
 
+impl EmailFormat for MultiPart {
+    fn format(&self, out: &mut Vec<u8>) {
+        write!(out, "{}", self.headers)
+            .expect("A Write implementation panicked while formatting headers");
+        out.extend_from_slice(b"\r\n");
+        self.format_body(out);
+    }
+}
+
 #[cfg(test)]
 mod test {
+    use pretty_assertions::assert_eq;
+
     use super::*;
     use crate::message::header;
 
@@ -477,7 +498,7 @@ mod test {
         assert_eq!(
             String::from_utf8(part.formatted()).unwrap(),
             concat!(
-                "Content-Type: multipart/mixed; \r\n",
+                "Content-Type: multipart/mixed;\r\n",
                 " boundary=\"0oVZ2r6AoLAhLlb0gPNSKy6BEqdS2IfwxrcbUuo1\"\r\n",
                 "\r\n",
                 "--0oVZ2r6AoLAhLlb0gPNSKy6BEqdS2IfwxrcbUuo1\r\n",
@@ -524,8 +545,8 @@ mod test {
         assert_eq!(
             String::from_utf8(part.formatted()).unwrap(),
             concat!(
-                "Content-Type: multipart/encrypted; \r\n",
-                " boundary=\"0oVZ2r6AoLAhLlb0gPNSKy6BEqdS2IfwxrcbUuo1\"; \r\n",
+                "Content-Type: multipart/encrypted;\r\n",
+                " boundary=\"0oVZ2r6AoLAhLlb0gPNSKy6BEqdS2IfwxrcbUuo1\";\r\n",
                 " protocol=\"application/pgp-encrypted\"\r\n",
                 "\r\n",
                 "--0oVZ2r6AoLAhLlb0gPNSKy6BEqdS2IfwxrcbUuo1\r\n",
@@ -580,8 +601,8 @@ mod test {
         assert_eq!(
             String::from_utf8(part.formatted()).unwrap(),
             concat!(
-                "Content-Type: multipart/signed; \r\n",
-                " boundary=\"0oVZ2r6AoLAhLlb0gPNSKy6BEqdS2IfwxrcbUuo1\"; \r\n",
+                "Content-Type: multipart/signed;\r\n",
+                " boundary=\"0oVZ2r6AoLAhLlb0gPNSKy6BEqdS2IfwxrcbUuo1\";\r\n",
                 " protocol=\"application/pgp-signature\";",
                 " micalg=\"pgp-sha256\"\r\n",
                 "\r\n",
@@ -622,7 +643,7 @@ mod test {
                              .body(String::from("<p>Текст <em>письма</em> в <a href=\"https://ru.wikipedia.org/wiki/Юникод\">уникоде</a><p>")));
 
         assert_eq!(String::from_utf8(part.formatted()).unwrap(),
-                   concat!("Content-Type: multipart/alternative; \r\n",
+                   concat!("Content-Type: multipart/alternative;\r\n",
                            " boundary=\"0oVZ2r6AoLAhLlb0gPNSKy6BEqdS2IfwxrcbUuo1\"\r\n",
                            "\r\n",
                            "--0oVZ2r6AoLAhLlb0gPNSKy6BEqdS2IfwxrcbUuo1\r\n",
@@ -660,11 +681,11 @@ mod test {
                              .body(String::from("int main() { return 0; }")));
 
         assert_eq!(String::from_utf8(part.formatted()).unwrap(),
-                   concat!("Content-Type: multipart/mixed; \r\n",
+                   concat!("Content-Type: multipart/mixed;\r\n",
                            " boundary=\"0oVZ2r6AoLAhLlb0gPNSKy6BEqdS2IfwxrcbUuo1\"\r\n",
                            "\r\n",
                            "--0oVZ2r6AoLAhLlb0gPNSKy6BEqdS2IfwxrcbUuo1\r\n",
-                           "Content-Type: multipart/related; \r\n",
+                           "Content-Type: multipart/related;\r\n",
                            " boundary=\"0oVZ2r6AoLAhLlb0gPNSKy6BEqdS2IfwxrcbUuo1\"\r\n",
                            "\r\n",
                            "--0oVZ2r6AoLAhLlb0gPNSKy6BEqdS2IfwxrcbUuo1\r\n",

src/message/mod.rs

@@ -14,7 +14,7 @@
 //! The easiest way of creating a message, which uses a plain text body.
 //!
 //! ```rust
-//! use lettre::message::Message;
+//! use lettre::message::{header::ContentType, Message};
 //!
 //! # use std::error::Error;
 //! # fn main() -> Result<(), Box<dyn Error>> {
@@ -23,6 +23,7 @@
 //!     .reply_to("Yuin <yuin@domain.tld>".parse()?)
 //!     .to("Hei <hei@domain.tld>".parse()?)
 //!     .subject("Happy new year")
+//!     .header(ContentType::TEXT_PLAIN)
 //!     .body(String::from("Be happy!"))?;
 //! # Ok(())
 //! # }
@@ -38,6 +39,7 @@
 //! To: Hei <hei@domain.tld>
 //! Subject: Happy new year
 //! Date: Sat, 12 Dec 2020 16:33:19 GMT
+//! Content-Type: text/plain; charset=utf-8
 //! Content-Transfer-Encoding: 7bit
 //!
 //! Be happy!
@@ -232,6 +234,7 @@ trait EmailFormat {
 pub struct MessageBuilder {
     headers: Headers,
     envelope: Option<Envelope>,
+    drop_bcc: bool,
 }
 
 impl MessageBuilder {
@@ -240,24 +243,26 @@ impl MessageBuilder {
         Self {
             headers: Headers::new(),
             envelope: None,
+            drop_bcc: true,
         }
     }
 
-    /// Set custom header to message
-    pub fn header<H: Header>(mut self, header: H) -> Self {
-        self.headers.set(header);
-        self
+    /// Set or add mailbox to `From` header
+    ///
+    /// Defined in [RFC5322](https://tools.ietf.org/html/rfc5322#section-3.6.2).
+    ///
+    /// Shortcut for `self.mailbox(header::From(mbox))`.
+    pub fn from(self, mbox: Mailbox) -> Self {
+        self.mailbox(header::From::from(Mailboxes::from(mbox)))
     }
 
-    /// Add mailbox to header
-    pub fn mailbox<H: Header + MailboxesHeader>(self, header: H) -> Self {
-        match self.headers.get::<H>() {
-            Some(mut header_) => {
-                header_.join_mailboxes(header);
-                self.header(header_)
-            }
-            None => self.header(header),
-        }
+    /// Set `Sender` header. Should be used when providing several `From` mailboxes.
+    ///
+    /// Defined in [RFC5322](https://tools.ietf.org/html/rfc5322#section-3.6.2).
+    ///
+    /// Shortcut for `self.header(header::Sender(mbox))`.
+    pub fn sender(self, mbox: Mailbox) -> Self {
+        self.header(header::Sender::from(mbox))
     }
 
     /// Add `Date` header to message
@@ -275,41 +280,6 @@ impl MessageBuilder {
         self.date(SystemTime::now())
     }
 
-    /// Set `Subject` header to message
-    ///
-    /// Shortcut for `self.header(header::Subject(subject.into()))`.
-    pub fn subject<S: Into<String>>(self, subject: S) -> Self {
-        let s: String = subject.into();
-        self.header(header::Subject::from(s))
-    }
-
-    /// Set `MIME-Version` header to 1.0
-    ///
-    /// Shortcut for `self.header(header::MIME_VERSION_1_0)`.
-    ///
-    /// Not exposed as it is set by body methods
-    fn mime_1_0(self) -> Self {
-        self.header(header::MIME_VERSION_1_0)
-    }
-
-    /// Set `Sender` header. Should be used when providing several `From` mailboxes.
-    ///
-    /// Defined in [RFC5322](https://tools.ietf.org/html/rfc5322#section-3.6.2).
-    ///
-    /// Shortcut for `self.header(header::Sender(mbox))`.
-    pub fn sender(self, mbox: Mailbox) -> Self {
-        self.header(header::Sender::from(mbox))
-    }
-
-    /// Set or add mailbox to `From` header
-    ///
-    /// Defined in [RFC5322](https://tools.ietf.org/html/rfc5322#section-3.6.2).
-    ///
-    /// Shortcut for `self.mailbox(header::From(mbox))`.
-    pub fn from(self, mbox: Mailbox) -> Self {
-        self.mailbox(header::From::from(Mailboxes::from(mbox)))
-    }
-
     /// Set or add mailbox to `ReplyTo` header
     ///
     /// Defined in [RFC5322](https://tools.ietf.org/html/rfc5322#section-3.6.2).
@@ -352,6 +322,14 @@ impl MessageBuilder {
         self.header(header::References::from(id))
     }
 
+    /// Set `Subject` header to message
+    ///
+    /// Shortcut for `self.header(header::Subject(subject.into()))`.
+    pub fn subject<S: Into<String>>(self, subject: S) -> Self {
+        let s: String = subject.into();
+        self.header(header::Subject::from(s))
+    }
+
     /// Set [Message-ID
     /// header](https://tools.ietf.org/html/rfc5322#section-3.6.4)
     ///
@@ -367,9 +345,9 @@ impl MessageBuilder {
                 let hostname = hostname::get()
                     .map_err(|_| ())
                     .and_then(|s| s.into_string().map_err(|_| ()))
-                    .unwrap_or_else(|_| DEFAULT_MESSAGE_ID_DOMAIN.to_string());
+                    .unwrap_or_else(|_| DEFAULT_MESSAGE_ID_DOMAIN.to_owned());
                 #[cfg(not(feature = "hostname"))]
-                let hostname = DEFAULT_MESSAGE_ID_DOMAIN.to_string();
+                let hostname = DEFAULT_MESSAGE_ID_DOMAIN.to_owned();
 
                 self.header(header::MessageId::from(
                     // https://tools.ietf.org/html/rfc5322#section-3.6.4
@@ -380,17 +358,48 @@ impl MessageBuilder {
     }
 
     /// Set [User-Agent
-    /// header](https://tools.ietf.org/html/draft-melnikov-email-user-agent-004)
+    /// header](https://tools.ietf.org/html/draft-melnikov-email-user-agent-00)
     pub fn user_agent(self, id: String) -> Self {
         self.header(header::UserAgent::from(id))
     }
 
+    /// Set custom header to message
+    pub fn header<H: Header>(mut self, header: H) -> Self {
+        self.headers.set(header);
+        self
+    }
+
+    /// Add mailbox to header
+    pub fn mailbox<H: Header + MailboxesHeader>(self, header: H) -> Self {
+        match self.headers.get::<H>() {
+            Some(mut header_) => {
+                header_.join_mailboxes(header);
+                self.header(header_)
+            }
+            None => self.header(header),
+        }
+    }
+
     /// Force specific envelope (by default it is derived from headers)
     pub fn envelope(mut self, envelope: Envelope) -> Self {
         self.envelope = Some(envelope);
         self
     }
 
+    /// Keep the `Bcc` header
+    ///
+    /// By default, the `Bcc` header is removed from the email after
+    /// using it to generate the message envelope. In some cases though,
+    /// like when saving the email as an `.eml`, or sending through
+    /// some transports (like the Gmail API) that don't take a separate
+    /// envelope value, it becomes necessary to keep the `Bcc` header.
+    ///
+    /// Calling this method overrides the default behavior.
+    pub fn keep_bcc(mut self) -> Self {
+        self.drop_bcc = false;
+        self
+    }
+
     // TODO: High-level methods for attachments and embedded files
 
     /// Create message from body
@@ -423,8 +432,10 @@ impl MessageBuilder {
             None => Envelope::try_from(&res.headers)?,
         };
 
-        // Remove `Bcc` headers now the envelope is set
-        res.headers.remove::<header::Bcc>();
+        if res.drop_bcc {
+            // Remove `Bcc` headers now the envelope is set
+            res.headers.remove::<header::Bcc>();
+        }
 
         Ok(Message {
             headers: res.headers,
@@ -455,6 +466,15 @@ impl MessageBuilder {
     pub fn singlepart(self, part: SinglePart) -> Result<Message, EmailError> {
         self.mime_1_0().build(MessageBody::Mime(Part::Single(part)))
     }
+
+    /// Set `MIME-Version` header to 1.0
+    ///
+    /// Shortcut for `self.header(header::MIME_VERSION_1_0)`.
+    ///
+    /// Not exposed as it is set by body methods
+    fn mime_1_0(self) -> Self {
+        self.header(header::MIME_VERSION_1_0)
+    }
 }
 
 /// Email message which can be formatted
@@ -483,6 +503,11 @@ impl Message {
         &self.headers
     }
 
+    /// Get a mutable reference to the headers
+    pub fn headers_mut(&mut self) -> &mut Headers {
+        &mut self.headers
+    }
+
     /// Get `Message` envelope
     pub fn envelope(&self) -> &Envelope {
         &self.envelope
@@ -500,7 +525,7 @@ impl Message {
     pub(crate) fn body_raw(&self) -> Vec<u8> {
         let mut out = Vec::new();
         match &self.body {
-            MessageBody::Mime(p) => p.format(&mut out),
+            MessageBody::Mime(p) => p.format_body(&mut out),
             MessageBody::Raw(r) => out.extend_from_slice(r),
         };
         out.extend_from_slice(b"\r\n");
@@ -521,7 +546,7 @@ impl Message {
     ///     .reply_to("Bob <bob@example.org>".parse().unwrap())
     ///     .to("Carla <carla@example.net>".parse().unwrap())
     ///     .subject("Hello")
-    ///     .body("Hi there, it's a test email, with utf-8 chars ë!\n\n\n".to_string())
+    ///     .body("Hi there, it's a test email, with utf-8 chars ë!\n\n\n".to_owned())
     ///     .unwrap();
     /// let key = "-----BEGIN RSA PRIVATE KEY-----
     /// MIIEowIBAAKCAQEAt2gawjoybf0mAz0mSX0cq1ah5F9cPazZdCwLnFBhRufxaZB8
@@ -550,10 +575,10 @@ impl Message {
     /// JcaBbL6ZSBIMA3AdaIjtvNRiomueHqh0GspTgOeCE2585TSFnw6vEOJ8RlR4A0Mw
     /// I45fbR4l+3D/30WMfZlM6bzZbwPXEnr2s1mirmuQpjumY9wLhK25
     /// -----END RSA PRIVATE KEY-----";
-    /// let signing_key = DkimSigningKey::new(key.to_string(), DkimSigningAlgorithm::Rsa).unwrap();
+    /// let signing_key = DkimSigningKey::new(key, DkimSigningAlgorithm::Rsa).unwrap();
     /// message.sign(&DkimConfig::default_config(
-    ///     "dkimtest".to_string(),
-    ///     "example.org".to_string(),
+    ///     "dkimtest".to_owned(),
+    ///     "example.org".to_owned(),
     ///     signing_key,
     /// ));
     /// println!(
@@ -598,6 +623,8 @@ fn make_message_id() -> String {
 mod test {
     use std::time::{Duration, SystemTime};
 
+    use pretty_assertions::assert_eq;
+
     use super::{header, mailbox::Mailbox, make_message_id, Message, MultiPart, SinglePart};
 
     #[test]
@@ -608,7 +635,7 @@ mod test {
     }
 
     #[test]
-    fn email_miminal_message() {
+    fn email_minimal_message() {
         assert!(Message::builder()
             .from("NoBody <nobody@domain.tld>".parse().unwrap())
             .to("NoBody <nobody@domain.tld>".parse().unwrap())
@@ -626,7 +653,7 @@ mod test {
     }
 
     #[test]
-    fn email_message() {
+    fn email_message_no_bcc() {
         // Tue, 15 Nov 1994 08:12:31 GMT
         let date = SystemTime::UNIX_EPOCH + Duration::from_secs(784887151);
 
@@ -661,6 +688,44 @@ mod test {
         );
     }
 
+    #[test]
+    fn email_message_keep_bcc() {
+        // Tue, 15 Nov 1994 08:12:31 GMT
+        let date = SystemTime::UNIX_EPOCH + Duration::from_secs(784887151);
+
+        let email = Message::builder()
+            .date(date)
+            .bcc("hidden@example.com".parse().unwrap())
+            .keep_bcc()
+            .header(header::From(
+                vec![Mailbox::new(
+                    Some("Каи".into()),
+                    "kayo@example.com".parse().unwrap(),
+                )]
+                .into(),
+            ))
+            .header(header::To(
+                vec!["Pony O.P. <pony@domain.tld>".parse().unwrap()].into(),
+            ))
+            .header(header::Subject::from(String::from("яңа ел белән!")))
+            .body(String::from("Happy new year!"))
+            .unwrap();
+
+        assert_eq!(
+            String::from_utf8(email.formatted()).unwrap(),
+            concat!(
+                "Date: Tue, 15 Nov 1994 08:12:31 +0000\r\n",
+                "Bcc: hidden@example.com\r\n",
+                "From: =?utf-8?b?0JrQsNC4?= <kayo@example.com>\r\n",
+                "To: \"Pony O.P.\" <pony@domain.tld>\r\n",
+                "Subject: =?utf-8?b?0Y/So9CwINC10Lsg0LHQtdC705nQvSE=?=\r\n",
+                "Content-Transfer-Encoding: 7bit\r\n",
+                "\r\n",
+                "Happy new year!"
+            )
+        );
+    }
+
     #[test]
     fn email_with_png() {
         // Tue, 15 Nov 1994 08:12:31 GMT

src/transport/file/error.rs

@@ -54,7 +54,7 @@ impl fmt::Debug for Error {
 
         builder.field("kind", &self.inner.kind);
 
-        if let Some(ref source) = self.inner.source {
+        if let Some(source) = &self.inner.source {
             builder.field("source", source);
         }
 
@@ -70,8 +70,8 @@ impl fmt::Display for Error {
             Kind::Envelope => f.write_str("internal client error")?,
         };
 
-        if let Some(ref e) = self.inner.source {
-            write!(f, ": {}", e)?;
+        if let Some(e) = &self.inner.source {
+            write!(f, ": {e}")?;
         }
 
         Ok(())

src/transport/file/mod.rs

@@ -157,7 +157,7 @@ mod error;
 type Id = String;
 
 /// Writes the content and the envelope information to a file
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 #[cfg_attr(docsrs, doc(cfg(feature = "file-transport")))]
 pub struct FileTransport {
@@ -167,7 +167,7 @@ pub struct FileTransport {
 }
 
 /// Asynchronously writes the content and the envelope information to a file
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 #[cfg_attr(docsrs, doc(cfg(any(feature = "tokio1", feature = "async-std1"))))]
 #[cfg(any(feature = "async-std1", feature = "tokio1"))]
@@ -208,18 +208,18 @@ impl FileTransport {
     pub fn read(&self, email_id: &str) -> Result<(Envelope, Vec<u8>), Error> {
         use std::fs;
 
-        let eml_file = self.path.join(format!("{}.eml", email_id));
+        let eml_file = self.path.join(format!("{email_id}.eml"));
         let eml = fs::read(eml_file).map_err(error::io)?;
 
-        let json_file = self.path.join(format!("{}.json", email_id));
-        let json = fs::read(&json_file).map_err(error::io)?;
+        let json_file = self.path.join(format!("{email_id}.json"));
+        let json = fs::read(json_file).map_err(error::io)?;
         let envelope = serde_json::from_slice(&json).map_err(error::envelope)?;
 
         Ok((envelope, eml))
     }
 
     fn path(&self, email_id: &Uuid, extension: &str) -> PathBuf {
-        self.path.join(format!("{}.{}", email_id, extension))
+        self.path.join(format!("{email_id}.{extension}"))
     }
 }
 
@@ -255,10 +255,10 @@ where
     /// Reads the envelope and the raw message content.
     #[cfg(feature = "file-transport-envelope")]
     pub async fn read(&self, email_id: &str) -> Result<(Envelope, Vec<u8>), Error> {
-        let eml_file = self.inner.path.join(format!("{}.eml", email_id));
+        let eml_file = self.inner.path.join(format!("{email_id}.eml"));
         let eml = E::fs_read(&eml_file).await.map_err(error::io)?;
 
-        let json_file = self.inner.path.join(format!("{}.json", email_id));
+        let json_file = self.inner.path.join(format!("{email_id}.json"));
         let json = E::fs_read(&json_file).await.map_err(error::io)?;
         let envelope = serde_json::from_slice(&json).map_err(error::envelope)?;
 
@@ -276,6 +276,8 @@ impl Transport for FileTransport {
         let email_id = Uuid::new_v4();
 
         let file = self.path(&email_id, "eml");
+        #[cfg(feature = "tracing")]
+        tracing::debug!(?file, "writing email to");
         fs::write(file, email).map_err(error::io)?;
 
         #[cfg(feature = "file-transport-envelope")]
@@ -306,6 +308,8 @@ where
         let email_id = Uuid::new_v4();
 
         let file = self.inner.path(&email_id, "eml");
+        #[cfg(feature = "tracing")]
+        tracing::debug!(?file, "writing email to");
         E::fs_write(&file, email).await.map_err(error::io)?;
 
         #[cfg(feature = "file-transport-envelope")]

src/transport/mod.rs

@@ -32,7 +32,7 @@
 //! | [`smtp`]     | SMTP     | [`SmtpTransport`]     | [`AsyncSmtpTransport`]     | Uses the SMTP protocol to send emails to a relay server |
 //! | [`sendmail`] | Sendmail | [`SendmailTransport`] | [`AsyncSendmailTransport`] | Uses the `sendmail` command to send emails              |
 //! | [`file`]     | File     | [`FileTransport`]     | [`AsyncFileTransport`]     | Saves the email as an `.eml` file                       |
-//! | [`stub`]     | Debug    | [`StubTransport`]     | [`StubTransport`]          | Drops the email - Useful for debugging                  |
+//! | [`stub`]     | Debug    | [`StubTransport`]     | [`AsyncStubTransport`]     | Drops the email - Useful for debugging                  |
 //!
 //! ## Building an email
 //!
@@ -65,7 +65,7 @@
 //!     .subject("Happy new year")
 //!     .body(String::from("Be happy!"))?;
 //!
-//! let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+//! let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 //!
 //! // Open a remote connection to the SMTP relay server
 //! let mailer = SmtpTransport::relay("smtp.gmail.com")?
@@ -75,7 +75,7 @@
 //! // Send the email
 //! match mailer.send(&email) {
 //!     Ok(_) => println!("Email sent successfully!"),
-//!     Err(e) => panic!("Could not send email: {:?}", e),
+//!     Err(e) => panic!("Could not send email: {e:?}"),
 //! }
 //! # Ok(())
 //! # }
@@ -97,6 +97,7 @@
 //! [`FileTransport`]: crate::FileTransport
 //! [`AsyncFileTransport`]: crate::AsyncFileTransport
 //! [`StubTransport`]: crate::transport::stub::StubTransport
+//! [`AsyncStubTransport`]: crate::transport::stub::AsyncStubTransport
 
 #[cfg(any(feature = "async-std1", feature = "tokio1"))]
 use async_trait::async_trait;
@@ -127,6 +128,9 @@ pub trait Transport {
     #[cfg(feature = "builder")]
     #[cfg_attr(docsrs, doc(cfg(feature = "builder")))]
     fn send(&self, message: &Message) -> Result<Self::Ok, Self::Error> {
+        #[cfg(feature = "tracing")]
+        tracing::trace!("starting to send an email");
+
         let raw = message.formatted();
         self.send_raw(message.envelope(), &raw)
     }
@@ -149,6 +153,9 @@ pub trait AsyncTransport {
     #[cfg_attr(docsrs, doc(cfg(feature = "builder")))]
     // TODO take &Message
     async fn send(&self, message: Message) -> Result<Self::Ok, Self::Error> {
+        #[cfg(feature = "tracing")]
+        tracing::trace!("starting to send an email");
+
         let raw = message.formatted();
         let envelope = message.envelope();
         self.send_raw(envelope, &raw).await

src/transport/sendmail/error.rs

@@ -52,7 +52,7 @@ impl fmt::Debug for Error {
 
         builder.field("kind", &self.inner.kind);
 
-        if let Some(ref source) = self.inner.source {
+        if let Some(source) = &self.inner.source {
             builder.field("source", source);
         }
 
@@ -67,8 +67,8 @@ impl fmt::Display for Error {
             Kind::Client => f.write_str("internal client error")?,
         };
 
-        if let Some(ref e) = self.inner.source {
-            write!(f, ": {}", e)?;
+        if let Some(e) = &self.inner.source {
+            write!(f, ": {e}")?;
         }
 
         Ok(())

src/transport/sendmail/mod.rs

@@ -232,6 +232,9 @@ impl Transport for SendmailTransport {
     type Error = Error;
 
     fn send_raw(&self, envelope: &Envelope, email: &[u8]) -> Result<Self::Ok, Self::Error> {
+        #[cfg(feature = "tracing")]
+        tracing::debug!(command = ?self.command, "sending email with");
+
         // Spawn the sendmail command
         let mut process = self.command(envelope).spawn().map_err(error::client)?;
 
@@ -261,6 +264,9 @@ impl AsyncTransport for AsyncSendmailTransport<AsyncStd1Executor> {
     async fn send_raw(&self, envelope: &Envelope, email: &[u8]) -> Result<Self::Ok, Self::Error> {
         use async_std::io::prelude::WriteExt;
 
+        #[cfg(feature = "tracing")]
+        tracing::debug!(command = ?self.inner.command, "sending email with");
+
         let mut command = self.async_std_command(envelope);
 
         // Spawn the sendmail command
@@ -293,6 +299,9 @@ impl AsyncTransport for AsyncSendmailTransport<Tokio1Executor> {
     async fn send_raw(&self, envelope: &Envelope, email: &[u8]) -> Result<Self::Ok, Self::Error> {
         use tokio1_crate::io::AsyncWriteExt;
 
+        #[cfg(feature = "tracing")]
+        tracing::debug!(command = ?self.inner.command, "sending email with");
+
         let mut command = self.tokio1_command(envelope);
 
         // Spawn the sendmail command

src/transport/smtp/async_transport.rs

@@ -1,7 +1,8 @@
+#[cfg(feature = "pool")]
+use std::sync::Arc;
 use std::{
     fmt::{self, Debug},
     marker::PhantomData,
-    sync::Arc,
     time::Duration,
 };
 
@@ -102,7 +103,7 @@ where
             .tls(Tls::Wrapper(tls_parameters)))
     }
 
-    /// Simple an secure transport, using STARTTLS to obtain encrypted connections
+    /// Simple and secure transport, using STARTTLS to obtain encrypted connections
     ///
     /// Alternative to [`AsyncSmtpTransport::relay`](#method.relay), for SMTP servers
     /// that don't take SMTPS connections.
@@ -150,28 +151,114 @@ where
     ///
     /// * No authentication
     /// * No TLS
-    /// * A 60 seconds timeout for smtp commands
+    /// * A 60-seconds timeout for smtp commands
     /// * Port 25
     ///
     /// Consider using [`AsyncSmtpTransport::relay`](#method.relay) or
     /// [`AsyncSmtpTransport::starttls_relay`](#method.starttls_relay) instead,
     /// if possible.
     pub fn builder_dangerous<T: Into<String>>(server: T) -> AsyncSmtpTransportBuilder {
-        let info = SmtpInfo {
-            server: server.into(),
-            ..Default::default()
-        };
-        AsyncSmtpTransportBuilder {
-            info,
-            #[cfg(feature = "pool")]
-            pool_config: PoolConfig::default(),
-        }
+        AsyncSmtpTransportBuilder::new(server)
+    }
+
+    /// Creates a `AsyncSmtpTransportBuilder` from a connection URL
+    ///
+    /// The protocol, credentials, host and port can be provided in a single URL.
+    /// Use the scheme `smtp` for an unencrypted relay (optionally in combination with the
+    /// `tls` parameter to allow/require STARTTLS) or `smtps` for SMTP over TLS.
+    /// The path section of the url can be used to set an alternative name for
+    /// the HELO / EHLO command.
+    /// For example `smtps://username:password@smtp.example.com/client.example.com:465`
+    /// will set the HELO / EHLO name `client.example.com`.
+    ///
+    /// <table>
+    ///   <thead>
+    ///     <tr>
+    ///       <th>scheme</th>
+    ///       <th>tls parameter</th>
+    ///       <th>example</th>
+    ///       <th>remarks</th>
+    ///     </tr>
+    ///   </thead>
+    ///   <tbody>
+    ///     <tr>
+    ///      <td>smtps</td>
+    ///      <td>-</td>
+    ///      <td>smtps://smtp.example.com</td>
+    ///      <td>SMTP over TLS, recommended method</td>
+    ///     </tr>
+    ///     <tr>
+    ///      <td>smtp</td>
+    ///      <td>required</td>
+    ///      <td>smtp://smtp.example.com?tls=required</td>
+    ///      <td>SMTP with STARTTLS required, when SMTP over TLS is not available</td>
+    ///     </tr>
+    ///     <tr>
+    ///      <td>smtp</td>
+    ///      <td>opportunistic</td>
+    ///      <td>smtp://smtp.example.com?tls=opportunistic</td>
+    ///      <td>
+    ///         SMTP with optionally STARTTLS when supported by the server.
+    ///         Caution: this method is vulnerable to a man-in-the-middle attack.
+    ///         Not recommended for production use.
+    ///       </td>
+    ///     </tr>
+    ///     <tr>
+    ///      <td>smtp</td>
+    ///      <td>-</td>
+    ///      <td>smtp://smtp.example.com</td>
+    ///      <td>Unencrypted SMTP, not recommended for production use.</td>
+    ///     </tr>
+    ///   </tbody>
+    /// </table>
+    ///
+    /// ```rust,no_run
+    /// use lettre::{
+    ///     message::header::ContentType, transport::smtp::authentication::Credentials,
+    ///     AsyncSmtpTransport, AsyncTransport, Message, Tokio1Executor,
+    /// };
+    /// # use tokio1_crate as tokio;
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    /// let email = Message::builder()
+    ///     .from("NoBody <nobody@domain.tld>".parse().unwrap())
+    ///     .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
+    ///     .to("Hei <hei@domain.tld>".parse().unwrap())
+    ///     .subject("Happy new year")
+    ///     .header(ContentType::TEXT_PLAIN)
+    ///     .body(String::from("Be happy!"))
+    ///     .unwrap();
+    ///
+    /// // Open a remote connection to gmail
+    /// let mailer: AsyncSmtpTransport<Tokio1Executor> =
+    ///     AsyncSmtpTransport::<Tokio1Executor>::from_url(
+    ///         "smtps://username:password@smtp.example.com:465",
+    ///     )
+    ///     .unwrap()
+    ///     .build();
+    ///
+    /// // Send the email
+    /// match mailer.send(email).await {
+    ///     Ok(_) => println!("Email sent successfully!"),
+    ///     Err(e) => panic!("Could not send email: {e:?}"),
+    /// }
+    /// # Ok(())
+    /// # }
+    /// ```
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+    )]
+    pub fn from_url(connection_url: &str) -> Result<AsyncSmtpTransportBuilder, Error> {
+        super::connection_url::from_connection_url(connection_url)
     }
 
     /// Tests the SMTP connection
     ///
     /// `test_connection()` tests the connection by using the SMTP NOOP command.
-    /// The connection is closed afterwards if a connection pool is not used.
+    /// The connection is closed afterward if a connection pool is not used.
     pub async fn test_connection(&self) -> Result<bool, Error> {
         let mut conn = self.inner.connection().await?;
 
@@ -198,6 +285,9 @@ where
 {
     fn clone(&self) -> Self {
         Self {
+            #[cfg(feature = "pool")]
+            inner: Arc::clone(&self.inner),
+            #[cfg(not(feature = "pool"))]
             inner: self.inner.clone(),
         }
     }
@@ -215,6 +305,20 @@ pub struct AsyncSmtpTransportBuilder {
 
 /// Builder for the SMTP `AsyncSmtpTransport`
 impl AsyncSmtpTransportBuilder {
+    // Create new builder with default parameters
+    pub(crate) fn new<T: Into<String>>(server: T) -> Self {
+        let info = SmtpInfo {
+            server: server.into(),
+            ..Default::default()
+        };
+
+        AsyncSmtpTransportBuilder {
+            info,
+            #[cfg(feature = "pool")]
+            pool_config: PoolConfig::default(),
+        }
+    }
+
     /// Set the name used during EHLO
     pub fn hello_name(mut self, name: ClientId) -> Self {
         self.info.hello_name = name;

src/transport/smtp/authentication.rs

@@ -51,7 +51,7 @@ pub enum Mechanism {
     /// [RFC 4616](https://tools.ietf.org/html/rfc4616)
     Plain,
     /// LOGIN authentication mechanism
-    /// Obsolete but needed for some providers (like office365)
+    /// Obsolete but needed for some providers (like Office 365)
     ///
     /// Defined in [draft-murchison-sasl-login-00](https://www.ietf.org/archive/id/draft-murchison-sasl-login-00.txt).
     Login,
@@ -71,7 +71,7 @@ impl Display for Mechanism {
 }
 
 impl Mechanism {
-    /// Does the mechanism supports initial response
+    /// Does the mechanism support initial response?
     pub fn supports_initial_response(self) -> bool {
         match self {
             Mechanism::Plain | Mechanism::Xoauth2 => true,
@@ -98,12 +98,14 @@ impl Mechanism {
                 let decoded_challenge = challenge
                     .ok_or_else(|| error::client("This mechanism does expect a challenge"))?;
 
-                if vec!["User Name", "Username:", "Username"].contains(&decoded_challenge) {
-                    return Ok(credentials.authentication_identity.to_string());
+                if ["User Name", "Username:", "Username", "User Name\0"]
+                    .contains(&decoded_challenge)
+                {
+                    return Ok(credentials.authentication_identity.clone());
                 }
 
-                if vec!["Password", "Password:"].contains(&decoded_challenge) {
-                    return Ok(credentials.secret.to_string());
+                if ["Password", "Password:", "Password\0"].contains(&decoded_challenge) {
+                    return Ok(credentials.secret.clone());
                 }
 
                 Err(error::client("Unrecognized challenge"))
@@ -127,7 +129,7 @@ mod test {
     fn test_plain() {
         let mechanism = Mechanism::Plain;
 
-        let credentials = Credentials::new("username".to_string(), "password".to_string());
+        let credentials = Credentials::new("username".to_owned(), "password".to_owned());
 
         assert_eq!(
             mechanism.response(&credentials, None).unwrap(),
@@ -140,7 +142,7 @@ mod test {
     fn test_login() {
         let mechanism = Mechanism::Login;
 
-        let credentials = Credentials::new("alice".to_string(), "wonderland".to_string());
+        let credentials = Credentials::new("alice".to_owned(), "wonderland".to_owned());
 
         assert_eq!(
             mechanism.response(&credentials, Some("Username")).unwrap(),
@@ -158,8 +160,8 @@ mod test {
         let mechanism = Mechanism::Xoauth2;
 
         let credentials = Credentials::new(
-            "username".to_string(),
-            "vF9dft4qmTc2Nvb3RlckBhdHRhdmlzdGEuY29tCg==".to_string(),
+            "username".to_owned(),
+            "vF9dft4qmTc2Nvb3RlckBhdHRhdmlzdGEuY29tCg==".to_owned(),
         );
 
         assert_eq!(
@@ -172,7 +174,7 @@ mod test {
     #[test]
     fn test_from_user_pass_for_credentials() {
         assert_eq!(
-            Credentials::new("alice".to_string(), "wonderland".to_string()),
+            Credentials::new("alice".to_owned(), "wonderland".to_owned()),
             Credentials::from(("alice", "wonderland"))
         );
     }

src/transport/smtp/client/async_connection.rs

@@ -1,14 +1,16 @@
-use std::{fmt::Display, time::Duration};
+use std::{fmt::Display, net::IpAddr, time::Duration};
 
 use futures_util::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
 
+#[cfg(feature = "tokio1")]
+use super::async_net::AsyncTokioStream;
 #[cfg(feature = "tracing")]
 use super::escape_crlf;
-use super::{AsyncNetworkStream, ClientCodec, TlsParameters};
+use super::{AsyncNetworkStream, ClientCodec, ConnectionState, TlsParameters};
 use crate::{
     transport::smtp::{
         authentication::{Credentials, Mechanism},
-        commands::*,
+        commands::{Auth, Data, Ehlo, Mail, Noop, Quit, Rcpt, Starttls},
         error,
         error::Error,
         extension::{ClientId, Extension, MailBodyParameter, MailParameter, ServerInfo},
@@ -17,45 +19,75 @@ use crate::{
     Envelope,
 };
 
-macro_rules! try_smtp (
-    ($err: expr, $client: ident) => ({
-        match $err {
-            Ok(val) => val,
-            Err(err) => {
-                $client.abort().await;
-                return Err(From::from(err))
-            },
-        }
-    })
-);
-
 /// Structure that implements the SMTP client
 pub struct AsyncSmtpConnection {
     /// TCP stream between client and server
     /// Value is None before connection
     stream: BufReader<AsyncNetworkStream>,
-    /// Panic state
-    panic: bool,
     /// Information about the server
     server_info: ServerInfo,
 }
 
 impl AsyncSmtpConnection {
+    /// Get information about the server
     pub fn server_info(&self) -> &ServerInfo {
         &self.server_info
     }
 
-    /// Connects to the configured server
+    /// Connects with existing async stream
     ///
     /// Sends EHLO and parses server information
     #[cfg(feature = "tokio1")]
+    pub async fn connect_with_transport(
+        stream: Box<dyn AsyncTokioStream>,
+        hello_name: &ClientId,
+    ) -> Result<AsyncSmtpConnection, Error> {
+        let stream = AsyncNetworkStream::use_existing_tokio1(stream);
+        Self::connect_impl(stream, hello_name).await
+    }
+
+    /// Connects to the configured server
+    ///
+    /// If `tls_parameters` is `Some`, then the connection will use Implicit TLS (sometimes
+    /// referred to as `SMTPS`). See also [`AsyncSmtpConnection::starttls`].
+    ///
+    /// If `local_address` is `Some`, then the address provided shall be used to bind the
+    /// connection to a specific local address using [`tokio1_crate::net::TcpSocket::bind`].
+    ///
+    /// Sends EHLO and parses server information
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use std::time::Duration;
+    /// # use lettre::transport::smtp::{client::{AsyncSmtpConnection, TlsParameters}, extension::ClientId};
+    /// # use tokio1_crate::{self as tokio, net::ToSocketAddrs as _};
+    /// #
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    /// let connection = AsyncSmtpConnection::connect_tokio1(
+    ///     ("example.com", 465),
+    ///     Some(Duration::from_secs(60)),
+    ///     &ClientId::default(),
+    ///     Some(TlsParameters::new("example.com".to_owned())?),
+    ///     None,
+    /// )
+    /// .await
+    /// .unwrap();
+    /// # Ok(())
+    /// # }
+    /// ```
+    #[cfg(feature = "tokio1")]
     pub async fn connect_tokio1<T: tokio1_crate::net::ToSocketAddrs>(
         server: T,
         timeout: Option<Duration>,
         hello_name: &ClientId,
         tls_parameters: Option<TlsParameters>,
+        local_address: Option<IpAddr>,
     ) -> Result<AsyncSmtpConnection, Error> {
-        let stream = AsyncNetworkStream::connect_tokio1(server, timeout, tls_parameters).await?;
+        let stream =
+            AsyncNetworkStream::connect_tokio1(server, timeout, tls_parameters, local_address)
+                .await?;
         Self::connect_impl(stream, hello_name).await
     }
 
@@ -80,7 +112,6 @@ impl AsyncSmtpConnection {
         let stream = BufReader::new(stream);
         let mut conn = AsyncSmtpConnection {
             stream,
-            panic: false,
             server_info: ServerInfo::default(),
         };
         // TODO log
@@ -114,7 +145,7 @@ impl AsyncSmtpConnection {
             mail_options.push(MailParameter::SmtpUtfEight);
         }
 
-        // Check for non-ascii content in message
+        // Check for non-ascii content in the message
         if !email.is_ascii() {
             if !self.server_info().supports_feature(Extension::EightBitMime) {
                 return Err(error::client(
@@ -124,50 +155,54 @@ impl AsyncSmtpConnection {
             mail_options.push(MailParameter::Body(MailBodyParameter::EightBitMime));
         }
 
-        try_smtp!(
-            self.command(Mail::new(envelope.from().cloned(), mail_options))
-                .await,
-            self
-        );
+        self.command(Mail::new(envelope.from().cloned(), mail_options))
+            .await?;
 
         // Recipient
         for to_address in envelope.to() {
-            try_smtp!(
-                self.command(Rcpt::new(to_address.clone(), vec![])).await,
-                self
-            );
+            self.command(Rcpt::new(to_address.clone(), vec![])).await?;
         }
 
         // Data
-        try_smtp!(self.command(Data).await, self);
+        self.command(Data).await?;
 
         // Message content
-        let result = try_smtp!(self.message(email).await, self);
-        Ok(result)
+        self.message(email).await
     }
 
     pub fn has_broken(&self) -> bool {
-        self.panic
+        match self.stream.get_ref().state() {
+            ConnectionState::Ok => false,
+            ConnectionState::Broken | ConnectionState::Closed => true,
+        }
     }
 
     pub fn can_starttls(&self) -> bool {
         !self.is_encrypted() && self.server_info.supports_feature(Extension::StartTls)
     }
 
+    /// Upgrade the connection using `STARTTLS`.
+    ///
+    /// As described in [rfc3207]. Note that this mechanism has been deprecated in [rfc8314].
+    ///
+    /// [rfc3207]: https://www.rfc-editor.org/rfc/rfc3207
+    /// [rfc8314]: https://www.rfc-editor.org/rfc/rfc8314
     #[allow(unused_variables)]
     pub async fn starttls(
-        &mut self,
+        mut self,
         tls_parameters: TlsParameters,
         hello_name: &ClientId,
-    ) -> Result<(), Error> {
+    ) -> Result<Self, Error> {
         if self.server_info.supports_feature(Extension::StartTls) {
-            try_smtp!(self.command(Starttls).await, self);
-            self.stream.get_mut().upgrade_tls(tls_parameters).await?;
+            self.command(Starttls).await?;
+            let stream = self.stream.into_inner();
+            let stream = stream.upgrade_tls(tls_parameters).await?;
+            self.stream = BufReader::new(stream);
             #[cfg(feature = "tracing")]
             tracing::debug!("connection encrypted");
             // Send EHLO again
-            try_smtp!(self.ehlo(hello_name).await, self);
-            Ok(())
+            self.ehlo(hello_name).await?;
+            Ok(self)
         } else {
             Err(error::client("STARTTLS is not supported on this server"))
         }
@@ -175,20 +210,23 @@ impl AsyncSmtpConnection {
 
     /// Send EHLO and update server info
     async fn ehlo(&mut self, hello_name: &ClientId) -> Result<(), Error> {
-        let ehlo_response = try_smtp!(self.command(Ehlo::new(hello_name.clone())).await, self);
-        self.server_info = try_smtp!(ServerInfo::from_response(&ehlo_response), self);
+        let ehlo_response = self.command(Ehlo::new(hello_name.clone())).await?;
+        self.server_info = ServerInfo::from_response(&ehlo_response)?;
         Ok(())
     }
 
     pub async fn quit(&mut self) -> Result<Response, Error> {
-        Ok(try_smtp!(self.command(Quit).await, self))
+        self.command(Quit).await
     }
 
     pub async fn abort(&mut self) {
-        // Only try to quit if we are not already broken
-        if !self.panic {
-            self.panic = true;
-            let _ = self.command(Quit).await;
+        match self.stream.get_ref().state() {
+            ConnectionState::Ok | ConnectionState::Broken => {
+                let _ = self.command(Quit).await;
+                let _ = self.stream.close().await;
+                self.stream.get_mut().set_state(ConnectionState::Closed);
+            }
+            ConnectionState::Closed => {}
         }
     }
 
@@ -207,7 +245,7 @@ impl AsyncSmtpConnection {
         self.command(Noop).await.is_ok()
     }
 
-    /// Sends an AUTH command with the given mechanism, and handles challenge if needed
+    /// Sends an AUTH command with the given mechanism, and handles the challenge if needed
     pub async fn auth(
         &mut self,
         mechanisms: &[Mechanism],
@@ -226,15 +264,13 @@ impl AsyncSmtpConnection {
 
         while challenges > 0 && response.has_code(334) {
             challenges -= 1;
-            response = try_smtp!(
-                self.command(Auth::new_from_response(
+            response = self
+                .command(Auth::new_from_response(
                     mechanism,
                     credentials.clone(),
                     &response,
                 )?)
-                .await,
-                self
-            );
+                .await?;
         }
 
         if challenges == 0 {
@@ -262,6 +298,9 @@ impl AsyncSmtpConnection {
 
     /// Writes a string to the server
     async fn write(&mut self, string: &[u8]) -> Result<(), Error> {
+        self.stream.get_ref().state().verify()?;
+        self.stream.get_mut().set_state(ConnectionState::Broken);
+
         self.stream
             .get_mut()
             .write_all(string)
@@ -273,6 +312,8 @@ impl AsyncSmtpConnection {
             .await
             .map_err(error::network)?;
 
+        self.stream.get_mut().set_state(ConnectionState::Ok);
+
         #[cfg(feature = "tracing")]
         tracing::debug!("Wrote: {}", escape_crlf(&String::from_utf8_lossy(string)));
         Ok(())
@@ -280,6 +321,9 @@ impl AsyncSmtpConnection {
 
     /// Gets the SMTP response
     pub async fn read_response(&mut self) -> Result<Response, Error> {
+        self.stream.get_ref().state().verify()?;
+        self.stream.get_mut().set_state(ConnectionState::Broken);
+
         let mut buffer = String::with_capacity(100);
 
         while self
@@ -293,14 +337,16 @@ impl AsyncSmtpConnection {
             tracing::debug!("<< {}", escape_crlf(&buffer));
             match parse_response(&buffer) {
                 Ok((_remaining, response)) => {
+                    self.stream.get_mut().set_state(ConnectionState::Ok);
+
                     return if response.is_positive() {
                         Ok(response)
                     } else {
                         Err(error::code(
                             response.code(),
-                            response.first_line().map(|s| s.to_owned()),
+                            Some(response.message().collect()),
                         ))
-                    }
+                    };
                 }
                 Err(nom::Err::Failure(e)) => {
                     return Err(error::response(e.to_string()));
@@ -316,7 +362,7 @@ impl AsyncSmtpConnection {
     }
 
     /// The X509 certificate of the server (DER encoded)
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
     pub fn peer_certificate(&self) -> Result<Vec<u8>, Error> {
         self.stream.get_ref().peer_certificate()
     }

src/transport/smtp/client/async_net.rs

@@ -1,6 +1,6 @@
 use std::{
-    io, mem,
-    net::SocketAddr,
+    fmt, io, mem,
+    net::{IpAddr, SocketAddr},
     pin::Pin,
     task::{Context, Poll},
     time::Duration,
@@ -11,15 +11,21 @@ use async_native_tls::TlsStream as AsyncStd1TlsStream;
 #[cfg(feature = "async-std1")]
 use async_std::net::{TcpStream as AsyncStd1TcpStream, ToSocketAddrs as AsyncStd1ToSocketAddrs};
 use futures_io::{
-    AsyncRead as FuturesAsyncRead, AsyncWrite as FuturesAsyncWrite, Error as IoError, ErrorKind,
-    Result as IoResult,
+    AsyncRead as FuturesAsyncRead, AsyncWrite as FuturesAsyncWrite, Result as IoResult,
 };
 #[cfg(feature = "async-std1-rustls-tls")]
 use futures_rustls::client::TlsStream as AsyncStd1RustlsTlsStream;
+#[cfg(any(feature = "tokio1-rustls-tls", feature = "async-std1-rustls-tls"))]
+use rustls::pki_types::ServerName;
+#[cfg(feature = "tokio1-boring-tls")]
+use tokio1_boring::SslStream as Tokio1SslStream;
 #[cfg(feature = "tokio1")]
-use tokio1_crate::io::{AsyncRead as _, AsyncWrite as _, ReadBuf as Tokio1ReadBuf};
+use tokio1_crate::io::{AsyncRead, AsyncWrite, ReadBuf as Tokio1ReadBuf};
 #[cfg(feature = "tokio1")]
-use tokio1_crate::net::{TcpStream as Tokio1TcpStream, ToSocketAddrs as Tokio1ToSocketAddrs};
+use tokio1_crate::net::{
+    TcpSocket as Tokio1TcpSocket, TcpStream as Tokio1TcpStream,
+    ToSocketAddrs as Tokio1ToSocketAddrs,
+};
 #[cfg(feature = "tokio1-native-tls")]
 use tokio1_native_tls_crate::TlsStream as Tokio1TlsStream;
 #[cfg(feature = "tokio1-rustls-tls")]
@@ -28,16 +34,33 @@ use tokio1_rustls::client::TlsStream as Tokio1RustlsTlsStream;
 #[cfg(any(
     feature = "tokio1-native-tls",
     feature = "tokio1-rustls-tls",
+    feature = "tokio1-boring-tls",
     feature = "async-std1-native-tls",
     feature = "async-std1-rustls-tls"
 ))]
 use super::InnerTlsParameters;
-use super::TlsParameters;
+use super::{ConnectionState, TlsParameters};
+#[cfg(feature = "tokio1")]
+use crate::transport::smtp::client::net::resolved_address_filter;
 use crate::transport::smtp::{error, Error};
 
 /// A network stream
+#[derive(Debug)]
 pub struct AsyncNetworkStream {
     inner: InnerAsyncNetworkStream,
+    state: ConnectionState,
+}
+
+#[cfg(feature = "tokio1")]
+pub trait AsyncTokioStream: AsyncRead + AsyncWrite + Send + Sync + Unpin + fmt::Debug {
+    fn peer_addr(&self) -> io::Result<SocketAddr>;
+}
+
+#[cfg(feature = "tokio1")]
+impl AsyncTokioStream for Tokio1TcpStream {
+    fn peer_addr(&self) -> io::Result<SocketAddr> {
+        self.peer_addr()
+    }
 }
 
 /// Represents the different types of underlying network streams
@@ -45,16 +68,20 @@ pub struct AsyncNetworkStream {
 // so clippy::large_enum_variant doesn't make sense here
 #[allow(clippy::large_enum_variant)]
 #[allow(dead_code)]
+#[derive(Debug)]
 enum InnerAsyncNetworkStream {
     /// Plain Tokio 1.x TCP stream
     #[cfg(feature = "tokio1")]
-    Tokio1Tcp(Tokio1TcpStream),
+    Tokio1Tcp(Box<dyn AsyncTokioStream>),
     /// Encrypted Tokio 1.x TCP stream
     #[cfg(feature = "tokio1-native-tls")]
-    Tokio1NativeTls(Tokio1TlsStream<Tokio1TcpStream>),
+    Tokio1NativeTls(Tokio1TlsStream<Box<dyn AsyncTokioStream>>),
     /// Encrypted Tokio 1.x TCP stream
     #[cfg(feature = "tokio1-rustls-tls")]
-    Tokio1RustlsTls(Tokio1RustlsTlsStream<Tokio1TcpStream>),
+    Tokio1RustlsTls(Tokio1RustlsTlsStream<Box<dyn AsyncTokioStream>>),
+    /// Encrypted Tokio 1.x TCP stream
+    #[cfg(feature = "tokio1-boring-tls")]
+    Tokio1BoringTls(Tokio1SslStream<Box<dyn AsyncTokioStream>>),
     /// Plain Tokio 1.x TCP stream
     #[cfg(feature = "async-std1")]
     AsyncStd1Tcp(AsyncStd1TcpStream),
@@ -64,92 +91,113 @@ enum InnerAsyncNetworkStream {
     /// Encrypted Tokio 1.x TCP stream
     #[cfg(feature = "async-std1-rustls-tls")]
     AsyncStd1RustlsTls(AsyncStd1RustlsTlsStream<AsyncStd1TcpStream>),
-    /// Can't be built
-    None,
 }
 
 impl AsyncNetworkStream {
     fn new(inner: InnerAsyncNetworkStream) -> Self {
-        if let InnerAsyncNetworkStream::None = inner {
-            debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
+        AsyncNetworkStream {
+            inner,
+            state: ConnectionState::Ok,
         }
+    }
 
-        AsyncNetworkStream { inner }
+    pub(super) fn state(&self) -> ConnectionState {
+        self.state
+    }
+
+    pub(super) fn set_state(&mut self, state: ConnectionState) {
+        self.state = state;
     }
 
     /// Returns peer's address
     pub fn peer_addr(&self) -> IoResult<SocketAddr> {
-        match self.inner {
+        match &self.inner {
             #[cfg(feature = "tokio1")]
-            InnerAsyncNetworkStream::Tokio1Tcp(ref s) => s.peer_addr(),
+            InnerAsyncNetworkStream::Tokio1Tcp(s) => s.peer_addr(),
             #[cfg(feature = "tokio1-native-tls")]
-            InnerAsyncNetworkStream::Tokio1NativeTls(ref s) => {
+            InnerAsyncNetworkStream::Tokio1NativeTls(s) => {
                 s.get_ref().get_ref().get_ref().peer_addr()
             }
             #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(ref s) => s.get_ref().0.peer_addr(),
+            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => s.get_ref().0.peer_addr(),
+            #[cfg(feature = "tokio1-boring-tls")]
+            InnerAsyncNetworkStream::Tokio1BoringTls(s) => s.get_ref().peer_addr(),
             #[cfg(feature = "async-std1")]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(ref s) => s.peer_addr(),
+            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => s.peer_addr(),
             #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(ref s) => s.get_ref().peer_addr(),
+            InnerAsyncNetworkStream::AsyncStd1NativeTls(s) => s.get_ref().peer_addr(),
             #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(ref s) => s.get_ref().0.peer_addr(),
-            InnerAsyncNetworkStream::None => {
-                debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
-                Err(IoError::new(
-                    ErrorKind::Other,
-                    "InnerAsyncNetworkStream::None must never be built",
-                ))
-            }
+            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => s.get_ref().0.peer_addr(),
         }
     }
 
+    #[cfg(feature = "tokio1")]
+    pub fn use_existing_tokio1(stream: Box<dyn AsyncTokioStream>) -> AsyncNetworkStream {
+        AsyncNetworkStream::new(InnerAsyncNetworkStream::Tokio1Tcp(stream))
+    }
+
     #[cfg(feature = "tokio1")]
     pub async fn connect_tokio1<T: Tokio1ToSocketAddrs>(
         server: T,
         timeout: Option<Duration>,
         tls_parameters: Option<TlsParameters>,
+        local_addr: Option<IpAddr>,
     ) -> Result<AsyncNetworkStream, Error> {
-        async fn try_connect_timeout<T: Tokio1ToSocketAddrs>(
+        async fn try_connect<T: Tokio1ToSocketAddrs>(
             server: T,
-            timeout: Duration,
+            timeout: Option<Duration>,
+            local_addr: Option<IpAddr>,
         ) -> Result<Tokio1TcpStream, Error> {
             let addrs = tokio1_crate::net::lookup_host(server)
                 .await
-                .map_err(error::connection)?;
+                .map_err(error::connection)?
+                .filter(|resolved_addr| resolved_address_filter(resolved_addr, local_addr));
 
             let mut last_err = None;
 
             for addr in addrs {
-                let connect_future = Tokio1TcpStream::connect(&addr);
-                match tokio1_crate::time::timeout(timeout, connect_future).await {
-                    Ok(Ok(stream)) => return Ok(stream),
-                    Ok(Err(err)) => last_err = Some(err),
-                    Err(_) => {
-                        last_err = Some(io::Error::new(
-                            io::ErrorKind::TimedOut,
-                            "connection timed out",
-                        ))
+                let socket = match addr.ip() {
+                    IpAddr::V4(_) => Tokio1TcpSocket::new_v4(),
+                    IpAddr::V6(_) => Tokio1TcpSocket::new_v6(),
+                }
+                .map_err(error::connection)?;
+                if let Some(local_addr) = local_addr {
+                    socket
+                        .bind(SocketAddr::new(local_addr, 0))
+                        .map_err(error::connection)?;
+                }
+
+                let connect_future = socket.connect(addr);
+                if let Some(timeout) = timeout {
+                    match tokio1_crate::time::timeout(timeout, connect_future).await {
+                        Ok(Ok(stream)) => return Ok(stream),
+                        Ok(Err(err)) => last_err = Some(err),
+                        Err(_) => {
+                            last_err = Some(io::Error::new(
+                                io::ErrorKind::TimedOut,
+                                "connection timed out",
+                            ))
+                        }
+                    }
+                } else {
+                    match connect_future.await {
+                        Ok(stream) => return Ok(stream),
+                        Err(err) => last_err = Some(err),
                     }
                 }
             }
 
             Err(match last_err {
                 Some(last_err) => error::connection(last_err),
-                None => error::connection("could not resolve to any address"),
+                None => error::connection("could not resolve to any supported address"),
             })
         }
 
-        let tcp_stream = match timeout {
-            Some(t) => try_connect_timeout(server, t).await?,
-            None => Tokio1TcpStream::connect(server)
-                .await
-                .map_err(error::connection)?,
-        };
-
-        let mut stream = AsyncNetworkStream::new(InnerAsyncNetworkStream::Tokio1Tcp(tcp_stream));
+        let tcp_stream = try_connect(server, timeout, local_addr).await?;
+        let mut stream =
+            AsyncNetworkStream::new(InnerAsyncNetworkStream::Tokio1Tcp(Box::new(tcp_stream)));
         if let Some(tls_parameters) = tls_parameters {
-            stream.upgrade_tls(tls_parameters).await?;
+            stream = stream.upgrade_tls(tls_parameters).await?;
         }
         Ok(stream)
     }
@@ -160,6 +208,9 @@ impl AsyncNetworkStream {
         timeout: Option<Duration>,
         tls_parameters: Option<TlsParameters>,
     ) -> Result<AsyncNetworkStream, Error> {
+        // Unfortunately, there doesn't currently seem to be a way to set the local address.
+        // Whilst we can create a AsyncStd1TcpStream from an existing socket, it needs to first have
+        // been connected, which is a blocking operation.
         async fn try_connect_timeout<T: AsyncStd1ToSocketAddrs>(
             server: T,
             timeout: Duration,
@@ -197,35 +248,39 @@ impl AsyncNetworkStream {
 
         let mut stream = AsyncNetworkStream::new(InnerAsyncNetworkStream::AsyncStd1Tcp(tcp_stream));
         if let Some(tls_parameters) = tls_parameters {
-            stream.upgrade_tls(tls_parameters).await?;
+            stream = stream.upgrade_tls(tls_parameters).await?;
         }
         Ok(stream)
     }
 
-    pub async fn upgrade_tls(&mut self, tls_parameters: TlsParameters) -> Result<(), Error> {
-        match &self.inner {
+    pub async fn upgrade_tls(self, tls_parameters: TlsParameters) -> Result<Self, Error> {
+        match self.inner {
             #[cfg(all(
                 feature = "tokio1",
-                not(any(feature = "tokio1-native-tls", feature = "tokio1-rustls-tls"))
+                not(any(
+                    feature = "tokio1-native-tls",
+                    feature = "tokio1-rustls-tls",
+                    feature = "tokio1-boring-tls"
+                ))
             ))]
             InnerAsyncNetworkStream::Tokio1Tcp(_) => {
                 let _ = tls_parameters;
                 panic!("Trying to upgrade an AsyncNetworkStream without having enabled either the tokio1-native-tls or the tokio1-rustls-tls feature");
             }
 
-            #[cfg(any(feature = "tokio1-native-tls", feature = "tokio1-rustls-tls"))]
-            InnerAsyncNetworkStream::Tokio1Tcp(_) => {
-                // get owned TcpStream
-                let tcp_stream = mem::replace(&mut self.inner, InnerAsyncNetworkStream::None);
-                let tcp_stream = match tcp_stream {
-                    InnerAsyncNetworkStream::Tokio1Tcp(tcp_stream) => tcp_stream,
-                    _ => unreachable!(),
-                };
-
-                self.inner = Self::upgrade_tokio1_tls(tcp_stream, tls_parameters)
+            #[cfg(any(
+                feature = "tokio1-native-tls",
+                feature = "tokio1-rustls-tls",
+                feature = "tokio1-boring-tls"
+            ))]
+            InnerAsyncNetworkStream::Tokio1Tcp(tcp_stream) => {
+                let inner = Self::upgrade_tokio1_tls(tcp_stream, tls_parameters)
                     .await
                     .map_err(error::connection)?;
-                Ok(())
+                Ok(Self {
+                    inner,
+                    state: ConnectionState::Ok,
+                })
             }
             #[cfg(all(
                 feature = "async-std1",
@@ -237,30 +292,30 @@ impl AsyncNetworkStream {
             }
 
             #[cfg(any(feature = "async-std1-native-tls", feature = "async-std1-rustls-tls"))]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(_) => {
-                // get owned TcpStream
-                let tcp_stream = mem::replace(&mut self.inner, InnerAsyncNetworkStream::None);
-                let tcp_stream = match tcp_stream {
-                    InnerAsyncNetworkStream::AsyncStd1Tcp(tcp_stream) => tcp_stream,
-                    _ => unreachable!(),
-                };
-
-                self.inner = Self::upgrade_asyncstd1_tls(tcp_stream, tls_parameters)
+            InnerAsyncNetworkStream::AsyncStd1Tcp(tcp_stream) => {
+                let inner = Self::upgrade_asyncstd1_tls(tcp_stream, tls_parameters)
                     .await
                     .map_err(error::connection)?;
-                Ok(())
+                Ok(Self {
+                    inner,
+                    state: ConnectionState::Ok,
+                })
             }
-            _ => Ok(()),
+            _ => Ok(self),
         }
     }
 
     #[allow(unused_variables)]
-    #[cfg(any(feature = "tokio1-native-tls", feature = "tokio1-rustls-tls"))]
+    #[cfg(any(
+        feature = "tokio1-native-tls",
+        feature = "tokio1-rustls-tls",
+        feature = "tokio1-boring-tls"
+    ))]
     async fn upgrade_tokio1_tls(
-        tcp_stream: Tokio1TcpStream,
+        tcp_stream: Box<dyn AsyncTokioStream>,
         tls_parameters: TlsParameters,
     ) -> Result<InnerAsyncNetworkStream, Error> {
-        let domain = tls_parameters.domain().to_string();
+        let domain = tls_parameters.domain().to_owned();
 
         match tls_parameters.connector {
             #[cfg(feature = "native-tls")]
@@ -287,7 +342,6 @@ impl AsyncNetworkStream {
 
                 #[cfg(feature = "tokio1-rustls-tls")]
                 return {
-                    use rustls::ServerName;
                     use tokio1_rustls::TlsConnector;
 
                     let domain = ServerName::try_from(domain.as_str())
@@ -295,17 +349,37 @@ impl AsyncNetworkStream {
 
                     let connector = TlsConnector::from(config);
                     let stream = connector
-                        .connect(domain, tcp_stream)
+                        .connect(domain.to_owned(), tcp_stream)
                         .await
                         .map_err(error::connection)?;
                     Ok(InnerAsyncNetworkStream::Tokio1RustlsTls(stream))
                 };
             }
+            #[cfg(feature = "boring-tls")]
+            InnerTlsParameters::BoringTls(connector) => {
+                #[cfg(not(feature = "tokio1-boring-tls"))]
+                panic!("built without the tokio1-boring-tls feature");
+
+                #[cfg(feature = "tokio1-boring-tls")]
+                return {
+                    let mut config = connector.configure().map_err(error::connection)?;
+                    config.set_verify_hostname(tls_parameters.accept_invalid_hostnames);
+
+                    let stream = tokio1_boring::connect(config, &domain, tcp_stream)
+                        .await
+                        .map_err(error::connection)?;
+                    Ok(InnerAsyncNetworkStream::Tokio1BoringTls(stream))
+                };
+            }
         }
     }
 
     #[allow(unused_variables)]
-    #[cfg(any(feature = "async-std1-native-tls", feature = "async-std1-rustls-tls"))]
+    #[cfg(any(
+        feature = "async-std1-native-tls",
+        feature = "async-std1-rustls-tls",
+        feature = "async-std1-boring-tls"
+    ))]
     async fn upgrade_asyncstd1_tls(
         tcp_stream: AsyncStd1TcpStream,
         mut tls_parameters: TlsParameters,
@@ -341,37 +415,41 @@ impl AsyncNetworkStream {
                 #[cfg(feature = "async-std1-rustls-tls")]
                 return {
                     use futures_rustls::TlsConnector;
-                    use rustls::ServerName;
 
                     let domain = ServerName::try_from(domain.as_str())
                         .map_err(|_| error::connection("domain isn't a valid DNS name"))?;
 
                     let connector = TlsConnector::from(config);
                     let stream = connector
-                        .connect(domain, tcp_stream)
+                        .connect(domain.to_owned(), tcp_stream)
                         .await
                         .map_err(error::connection)?;
                     Ok(InnerAsyncNetworkStream::AsyncStd1RustlsTls(stream))
                 };
             }
+            #[cfg(feature = "boring-tls")]
+            InnerTlsParameters::BoringTls(connector) => {
+                panic!("boring-tls isn't supported with async-std yet.");
+            }
         }
     }
 
     pub fn is_encrypted(&self) -> bool {
-        match self.inner {
+        match &self.inner {
             #[cfg(feature = "tokio1")]
             InnerAsyncNetworkStream::Tokio1Tcp(_) => false,
             #[cfg(feature = "tokio1-native-tls")]
             InnerAsyncNetworkStream::Tokio1NativeTls(_) => true,
             #[cfg(feature = "tokio1-rustls-tls")]
             InnerAsyncNetworkStream::Tokio1RustlsTls(_) => true,
+            #[cfg(feature = "tokio1-boring-tls")]
+            InnerAsyncNetworkStream::Tokio1BoringTls(_) => true,
             #[cfg(feature = "async-std1")]
             InnerAsyncNetworkStream::AsyncStd1Tcp(_) => false,
             #[cfg(feature = "async-std1-native-tls")]
             InnerAsyncNetworkStream::AsyncStd1NativeTls(_) => true,
             #[cfg(feature = "async-std1-rustls-tls")]
             InnerAsyncNetworkStream::AsyncStd1RustlsTls(_) => true,
-            InnerAsyncNetworkStream::None => false,
         }
     }
 
@@ -397,8 +475,14 @@ impl AsyncNetworkStream {
                 .unwrap()
                 .first()
                 .unwrap()
-                .clone()
-                .0),
+                .to_vec()),
+            #[cfg(feature = "tokio1-boring-tls")]
+            InnerAsyncNetworkStream::Tokio1BoringTls(stream) => Ok(stream
+                .ssl()
+                .peer_certificate()
+                .unwrap()
+                .to_der()
+                .map_err(error::tls)?),
             #[cfg(feature = "async-std1")]
             InnerAsyncNetworkStream::AsyncStd1Tcp(_) => {
                 Err(error::client("Connection is not encrypted"))
@@ -413,9 +497,7 @@ impl AsyncNetworkStream {
                 .unwrap()
                 .first()
                 .unwrap()
-                .clone()
-                .0),
-            InnerAsyncNetworkStream::None => panic!("InnerNetworkStream::None must never be built"),
+                .to_vec()),
         }
     }
 }
@@ -426,9 +508,9 @@ impl FuturesAsyncRead for AsyncNetworkStream {
         cx: &mut Context<'_>,
         buf: &mut [u8],
     ) -> Poll<IoResult<usize>> {
-        match self.inner {
+        match &mut self.inner {
             #[cfg(feature = "tokio1")]
-            InnerAsyncNetworkStream::Tokio1Tcp(ref mut s) => {
+            InnerAsyncNetworkStream::Tokio1Tcp(s) => {
                 let mut b = Tokio1ReadBuf::new(buf);
                 match Pin::new(s).poll_read(cx, &mut b) {
                     Poll::Ready(Ok(())) => Poll::Ready(Ok(b.filled().len())),
@@ -437,7 +519,7 @@ impl FuturesAsyncRead for AsyncNetworkStream {
                 }
             }
             #[cfg(feature = "tokio1-native-tls")]
-            InnerAsyncNetworkStream::Tokio1NativeTls(ref mut s) => {
+            InnerAsyncNetworkStream::Tokio1NativeTls(s) => {
                 let mut b = Tokio1ReadBuf::new(buf);
                 match Pin::new(s).poll_read(cx, &mut b) {
                     Poll::Ready(Ok(())) => Poll::Ready(Ok(b.filled().len())),
@@ -446,7 +528,16 @@ impl FuturesAsyncRead for AsyncNetworkStream {
                 }
             }
             #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(ref mut s) => {
+            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => {
+                let mut b = Tokio1ReadBuf::new(buf);
+                match Pin::new(s).poll_read(cx, &mut b) {
+                    Poll::Ready(Ok(())) => Poll::Ready(Ok(b.filled().len())),
+                    Poll::Ready(Err(err)) => Poll::Ready(Err(err)),
+                    Poll::Pending => Poll::Pending,
+                }
+            }
+            #[cfg(feature = "tokio1-boring-tls")]
+            InnerAsyncNetworkStream::Tokio1BoringTls(s) => {
                 let mut b = Tokio1ReadBuf::new(buf);
                 match Pin::new(s).poll_read(cx, &mut b) {
                     Poll::Ready(Ok(())) => Poll::Ready(Ok(b.filled().len())),
@@ -455,19 +546,11 @@ impl FuturesAsyncRead for AsyncNetworkStream {
                 }
             }
             #[cfg(feature = "async-std1")]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(ref mut s) => Pin::new(s).poll_read(cx, buf),
+            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => Pin::new(s).poll_read(cx, buf),
             #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(ref mut s) => {
-                Pin::new(s).poll_read(cx, buf)
-            }
+            InnerAsyncNetworkStream::AsyncStd1NativeTls(s) => Pin::new(s).poll_read(cx, buf),
             #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(ref mut s) => {
-                Pin::new(s).poll_read(cx, buf)
-            }
-            InnerAsyncNetworkStream::None => {
-                debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
-                Poll::Ready(Ok(0))
-            }
+            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => Pin::new(s).poll_read(cx, buf),
         }
     }
 }
@@ -478,69 +561,61 @@ impl FuturesAsyncWrite for AsyncNetworkStream {
         cx: &mut Context<'_>,
         buf: &[u8],
     ) -> Poll<IoResult<usize>> {
-        match self.inner {
+        match &mut self.inner {
             #[cfg(feature = "tokio1")]
-            InnerAsyncNetworkStream::Tokio1Tcp(ref mut s) => Pin::new(s).poll_write(cx, buf),
+            InnerAsyncNetworkStream::Tokio1Tcp(s) => Pin::new(s).poll_write(cx, buf),
             #[cfg(feature = "tokio1-native-tls")]
-            InnerAsyncNetworkStream::Tokio1NativeTls(ref mut s) => Pin::new(s).poll_write(cx, buf),
+            InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_write(cx, buf),
             #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(ref mut s) => Pin::new(s).poll_write(cx, buf),
+            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => Pin::new(s).poll_write(cx, buf),
+            #[cfg(feature = "tokio1-boring-tls")]
+            InnerAsyncNetworkStream::Tokio1BoringTls(s) => Pin::new(s).poll_write(cx, buf),
             #[cfg(feature = "async-std1")]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(ref mut s) => Pin::new(s).poll_write(cx, buf),
+            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => Pin::new(s).poll_write(cx, buf),
             #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(ref mut s) => {
-                Pin::new(s).poll_write(cx, buf)
-            }
+            InnerAsyncNetworkStream::AsyncStd1NativeTls(s) => Pin::new(s).poll_write(cx, buf),
             #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(ref mut s) => {
-                Pin::new(s).poll_write(cx, buf)
-            }
-            InnerAsyncNetworkStream::None => {
-                debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
-                Poll::Ready(Ok(0))
-            }
+            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => Pin::new(s).poll_write(cx, buf),
         }
     }
 
     fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<IoResult<()>> {
-        match self.inner {
+        match &mut self.inner {
             #[cfg(feature = "tokio1")]
-            InnerAsyncNetworkStream::Tokio1Tcp(ref mut s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::Tokio1Tcp(s) => Pin::new(s).poll_flush(cx),
             #[cfg(feature = "tokio1-native-tls")]
-            InnerAsyncNetworkStream::Tokio1NativeTls(ref mut s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_flush(cx),
             #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(ref mut s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => Pin::new(s).poll_flush(cx),
+            #[cfg(feature = "tokio1-boring-tls")]
+            InnerAsyncNetworkStream::Tokio1BoringTls(s) => Pin::new(s).poll_flush(cx),
             #[cfg(feature = "async-std1")]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(ref mut s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => Pin::new(s).poll_flush(cx),
             #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(ref mut s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::AsyncStd1NativeTls(s) => Pin::new(s).poll_flush(cx),
             #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(ref mut s) => Pin::new(s).poll_flush(cx),
-            InnerAsyncNetworkStream::None => {
-                debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
-                Poll::Ready(Ok(()))
-            }
+            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => Pin::new(s).poll_flush(cx),
         }
     }
 
     fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<IoResult<()>> {
-        match self.inner {
+        self.state = ConnectionState::Closed;
+
+        match &mut self.inner {
             #[cfg(feature = "tokio1")]
-            InnerAsyncNetworkStream::Tokio1Tcp(ref mut s) => Pin::new(s).poll_shutdown(cx),
+            InnerAsyncNetworkStream::Tokio1Tcp(s) => Pin::new(s).poll_shutdown(cx),
             #[cfg(feature = "tokio1-native-tls")]
-            InnerAsyncNetworkStream::Tokio1NativeTls(ref mut s) => Pin::new(s).poll_shutdown(cx),
+            InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_shutdown(cx),
             #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(ref mut s) => Pin::new(s).poll_shutdown(cx),
+            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => Pin::new(s).poll_shutdown(cx),
+            #[cfg(feature = "tokio1-boring-tls")]
+            InnerAsyncNetworkStream::Tokio1BoringTls(s) => Pin::new(s).poll_shutdown(cx),
             #[cfg(feature = "async-std1")]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(ref mut s) => Pin::new(s).poll_close(cx),
+            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => Pin::new(s).poll_close(cx),
             #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(ref mut s) => Pin::new(s).poll_close(cx),
+            InnerAsyncNetworkStream::AsyncStd1NativeTls(s) => Pin::new(s).poll_close(cx),
             #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(ref mut s) => Pin::new(s).poll_close(cx),
-            InnerAsyncNetworkStream::None => {
-                debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
-                Poll::Ready(Ok(()))
-            }
+            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => Pin::new(s).poll_close(cx),
         }
     }
 }

src/transport/smtp/client/connection.rs

@@ -1,18 +1,18 @@
 use std::{
     fmt::Display,
     io::{self, BufRead, BufReader, Write},
-    net::ToSocketAddrs,
+    net::{IpAddr, ToSocketAddrs},
     time::Duration,
 };
 
 #[cfg(feature = "tracing")]
 use super::escape_crlf;
-use super::{ClientCodec, NetworkStream, TlsParameters};
+use super::{ClientCodec, ConnectionState, NetworkStream, TlsParameters};
 use crate::{
     address::Envelope,
     transport::smtp::{
         authentication::{Credentials, Mechanism},
-        commands::*,
+        commands::{Auth, Data, Ehlo, Mail, Noop, Quit, Rcpt, Starttls},
         error,
         error::Error,
         extension::{ClientId, Extension, MailBodyParameter, MailParameter, ServerInfo},
@@ -20,30 +20,17 @@ use crate::{
     },
 };
 
-macro_rules! try_smtp (
-    ($err: expr, $client: ident) => ({
-        match $err {
-            Ok(val) => val,
-            Err(err) => {
-                $client.abort();
-                return Err(From::from(err))
-            },
-        }
-    })
-);
-
 /// Structure that implements the SMTP client
 pub struct SmtpConnection {
     /// TCP stream between client and server
     /// Value is None before connection
     stream: BufReader<NetworkStream>,
-    /// Panic state
-    panic: bool,
     /// Information about the server
     server_info: ServerInfo,
 }
 
 impl SmtpConnection {
+    /// Get information about the server
     pub fn server_info(&self) -> &ServerInfo {
         &self.server_info
     }
@@ -58,12 +45,12 @@ impl SmtpConnection {
         timeout: Option<Duration>,
         hello_name: &ClientId,
         tls_parameters: Option<&TlsParameters>,
+        local_address: Option<IpAddr>,
     ) -> Result<SmtpConnection, Error> {
-        let stream = NetworkStream::connect(server, timeout, tls_parameters)?;
+        let stream = NetworkStream::connect(server, timeout, tls_parameters, local_address)?;
         let stream = BufReader::new(stream);
         let mut conn = SmtpConnection {
             stream,
-            panic: false,
             server_info: ServerInfo::default(),
         };
         conn.set_timeout(timeout).map_err(error::network)?;
@@ -98,7 +85,7 @@ impl SmtpConnection {
             mail_options.push(MailParameter::SmtpUtfEight);
         }
 
-        // Check for non-ascii content in message
+        // Check for non-ascii content in the message
         if !email.is_ascii() {
             if !self.server_info().supports_feature(Extension::EightBitMime) {
                 return Err(error::client(
@@ -108,26 +95,25 @@ impl SmtpConnection {
             mail_options.push(MailParameter::Body(MailBodyParameter::EightBitMime));
         }
 
-        try_smtp!(
-            self.command(Mail::new(envelope.from().cloned(), mail_options)),
-            self
-        );
+        self.command(Mail::new(envelope.from().cloned(), mail_options))?;
 
         // Recipient
         for to_address in envelope.to() {
-            try_smtp!(self.command(Rcpt::new(to_address.clone(), vec![])), self);
+            self.command(Rcpt::new(to_address.clone(), vec![]))?;
         }
 
         // Data
-        try_smtp!(self.command(Data), self);
+        self.command(Data)?;
 
         // Message content
-        let result = try_smtp!(self.message(email), self);
-        Ok(result)
+        self.message(email)
     }
 
     pub fn has_broken(&self) -> bool {
-        self.panic
+        match self.stream.get_ref().state() {
+            ConnectionState::Ok => false,
+            ConnectionState::Broken | ConnectionState::Closed => true,
+        }
     }
 
     pub fn can_starttls(&self) -> bool {
@@ -136,22 +122,28 @@ impl SmtpConnection {
 
     #[allow(unused_variables)]
     pub fn starttls(
-        &mut self,
+        mut self,
         tls_parameters: &TlsParameters,
         hello_name: &ClientId,
-    ) -> Result<(), Error> {
+    ) -> Result<Self, Error> {
         if self.server_info.supports_feature(Extension::StartTls) {
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
             {
-                try_smtp!(self.command(Starttls), self);
-                self.stream.get_mut().upgrade_tls(tls_parameters)?;
+                self.command(Starttls)?;
+                let stream = self.stream.into_inner();
+                let stream = stream.upgrade_tls(tls_parameters)?;
+                self.stream = BufReader::new(stream);
                 #[cfg(feature = "tracing")]
                 tracing::debug!("connection encrypted");
                 // Send EHLO again
-                try_smtp!(self.ehlo(hello_name), self);
-                Ok(())
+                self.ehlo(hello_name)?;
+                Ok(self)
             }
-            #[cfg(not(any(feature = "native-tls", feature = "rustls-tls")))]
+            #[cfg(not(any(
+                feature = "native-tls",
+                feature = "rustls-tls",
+                feature = "boring-tls"
+            )))]
             // This should never happen as `Tls` can only be created
             // when a TLS library is enabled
             unreachable!("TLS support required but not supported");
@@ -162,20 +154,23 @@ impl SmtpConnection {
 
     /// Send EHLO and update server info
     fn ehlo(&mut self, hello_name: &ClientId) -> Result<(), Error> {
-        let ehlo_response = try_smtp!(self.command(Ehlo::new(hello_name.clone())), self);
-        self.server_info = try_smtp!(ServerInfo::from_response(&ehlo_response), self);
+        let ehlo_response = self.command(Ehlo::new(hello_name.clone()))?;
+        self.server_info = ServerInfo::from_response(&ehlo_response)?;
         Ok(())
     }
 
     pub fn quit(&mut self) -> Result<Response, Error> {
-        Ok(try_smtp!(self.command(Quit), self))
+        self.command(Quit)
     }
 
     pub fn abort(&mut self) {
-        // Only try to quit if we are not already broken
-        if !self.panic {
-            self.panic = true;
-            let _ = self.command(Quit);
+        match self.stream.get_ref().state() {
+            ConnectionState::Ok | ConnectionState::Broken => {
+                let _ = self.command(Quit);
+                let _ = self.stream.get_mut().shutdown(std::net::Shutdown::Both);
+                self.stream.get_mut().set_state(ConnectionState::Closed);
+            }
+            ConnectionState::Closed => {}
         }
     }
 
@@ -200,7 +195,7 @@ impl SmtpConnection {
         self.command(Noop).is_ok()
     }
 
-    /// Sends an AUTH command with the given mechanism, and handles challenge if needed
+    /// Sends an AUTH command with the given mechanism, and handles the challenge if needed
     pub fn auth(
         &mut self,
         mechanisms: &[Mechanism],
@@ -217,14 +212,11 @@ impl SmtpConnection {
 
         while challenges > 0 && response.has_code(334) {
             challenges -= 1;
-            response = try_smtp!(
-                self.command(Auth::new_from_response(
-                    mechanism,
-                    credentials.clone(),
-                    &response,
-                )?),
-                self
-            );
+            response = self.command(Auth::new_from_response(
+                mechanism,
+                credentials.clone(),
+                &response,
+            )?)?;
         }
 
         if challenges == 0 {
@@ -236,11 +228,12 @@ impl SmtpConnection {
 
     /// Sends the message content
     pub fn message(&mut self, message: &[u8]) -> Result<Response, Error> {
-        let mut out_buf: Vec<u8> = vec![];
         let mut codec = ClientCodec::new();
+        let mut out_buf = Vec::with_capacity(message.len());
         codec.encode(message, &mut out_buf);
         self.write(out_buf.as_slice())?;
         self.write(b"\r\n.\r\n")?;
+
         self.read_response()
     }
 
@@ -252,12 +245,17 @@ impl SmtpConnection {
 
     /// Writes a string to the server
     fn write(&mut self, string: &[u8]) -> Result<(), Error> {
+        self.stream.get_ref().state().verify()?;
+        self.stream.get_mut().set_state(ConnectionState::Broken);
+
         self.stream
             .get_mut()
             .write_all(string)
             .map_err(error::network)?;
         self.stream.get_mut().flush().map_err(error::network)?;
 
+        self.stream.get_mut().set_state(ConnectionState::Ok);
+
         #[cfg(feature = "tracing")]
         tracing::debug!("Wrote: {}", escape_crlf(&String::from_utf8_lossy(string)));
         Ok(())
@@ -265,6 +263,9 @@ impl SmtpConnection {
 
     /// Gets the SMTP response
     pub fn read_response(&mut self) -> Result<Response, Error> {
+        self.stream.get_ref().state().verify()?;
+        self.stream.get_mut().set_state(ConnectionState::Broken);
+
         let mut buffer = String::with_capacity(100);
 
         while self.stream.read_line(&mut buffer).map_err(error::network)? > 0 {
@@ -272,12 +273,14 @@ impl SmtpConnection {
             tracing::debug!("<< {}", escape_crlf(&buffer));
             match parse_response(&buffer) {
                 Ok((_remaining, response)) => {
+                    self.stream.get_mut().set_state(ConnectionState::Ok);
+
                     return if response.is_positive() {
                         Ok(response)
                     } else {
                         Err(error::code(
                             response.code(),
-                            response.first_line().map(|s| s.to_owned()),
+                            Some(response.message().collect()),
                         ))
                     };
                 }
@@ -295,7 +298,7 @@ impl SmtpConnection {
     }
 
     /// The X509 certificate of the server (DER encoded)
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
     pub fn peer_certificate(&self) -> Result<Vec<u8>, Error> {
         self.stream.get_ref().peer_certificate()
     }

src/transport/smtp/client/mod.rs

@@ -11,8 +11,8 @@
 //!     client::SmtpConnection, commands::*, extension::ClientId, SMTP_PORT,
 //! };
 //!
-//! let hello = ClientId::Domain("my_hostname".to_string());
-//! let mut client = SmtpConnection::connect(&("localhost", SMTP_PORT), None, &hello, None)?;
+//! let hello = ClientId::Domain("my_hostname".to_owned());
+//! let mut client = SmtpConnection::connect(&("localhost", SMTP_PORT), None, &hello, None, None)?;
 //! client.command(Mail::new(Some("user@example.com".parse()?), vec![]))?;
 //! client.command(Rcpt::new("user@example.org".parse()?, vec![]))?;
 //! client.command(Data)?;
@@ -29,13 +29,18 @@ use std::fmt::Debug;
 pub use self::async_connection::AsyncSmtpConnection;
 #[cfg(any(feature = "tokio1", feature = "async-std1"))]
 pub use self::async_net::AsyncNetworkStream;
+#[cfg(feature = "tokio1")]
+pub use self::async_net::AsyncTokioStream;
 use self::net::NetworkStream;
-#[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
 pub(super) use self::tls::InnerTlsParameters;
+#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+pub use self::tls::TlsVersion;
 pub use self::{
     connection::SmtpConnection,
-    tls::{Certificate, Tls, TlsParameters, TlsParametersBuilder},
+    tls::{Certificate, CertificateStore, Tls, TlsParameters, TlsParametersBuilder},
 };
+use super::{error, Error};
 
 #[cfg(any(feature = "tokio1", feature = "async-std1"))]
 mod async_connection;
@@ -45,61 +50,75 @@ mod connection;
 mod net;
 mod tls;
 
+#[derive(Debug, Copy, Clone)]
+enum ConnectionState {
+    Ok,
+    Broken,
+    Closed,
+}
+
+impl ConnectionState {
+    fn verify(&mut self) -> Result<(), Error> {
+        match self {
+            Self::Ok => Ok(()),
+            Self::Broken => Err(error::connection("connection broken")),
+            Self::Closed => Err(error::connection("connection closed")),
+        }
+    }
+}
+
 /// The codec used for transparency
-#[derive(Default, Clone, Copy, Debug)]
-#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[derive(Debug)]
 struct ClientCodec {
-    escape_count: u8,
+    status: CodecStatus,
 }
 
 impl ClientCodec {
     /// Creates a new client codec
     pub fn new() -> Self {
-        ClientCodec::default()
+        Self {
+            status: CodecStatus::StartOfNewLine,
+        }
     }
 
     /// Adds transparency
     fn encode(&mut self, frame: &[u8], buf: &mut Vec<u8>) {
-        match frame.len() {
-            0 => {
-                match self.escape_count {
-                    0 => buf.extend_from_slice(b"\r\n.\r\n"),
-                    1 => buf.extend_from_slice(b"\n.\r\n"),
-                    2 => buf.extend_from_slice(b".\r\n"),
-                    _ => unreachable!(),
+        for &b in frame {
+            buf.push(b);
+            match (b, self.status) {
+                (b'\r', _) => {
+                    self.status = CodecStatus::StartingNewLine;
                 }
-                self.escape_count = 0;
-            }
-            _ => {
-                let mut start = 0;
-                for (idx, byte) in frame.iter().enumerate() {
-                    match self.escape_count {
-                        0 => self.escape_count = if *byte == b'\r' { 1 } else { 0 },
-                        1 => self.escape_count = if *byte == b'\n' { 2 } else { 0 },
-                        2 => {
-                            self.escape_count = if *byte == b'.' {
-                                3
-                            } else if *byte == b'\r' {
-                                1
-                            } else {
-                                0
-                            }
-                        }
-                        _ => unreachable!(),
-                    }
-                    if self.escape_count == 3 {
-                        self.escape_count = 0;
-                        buf.extend_from_slice(&frame[start..idx]);
-                        buf.extend_from_slice(b".");
-                        start = idx;
-                    }
+                (b'\n', CodecStatus::StartingNewLine) => {
+                    self.status = CodecStatus::StartOfNewLine;
                 }
-                buf.extend_from_slice(&frame[start..]);
+                (_, CodecStatus::StartingNewLine) => {
+                    self.status = CodecStatus::MiddleOfLine;
+                }
+                (b'.', CodecStatus::StartOfNewLine) => {
+                    self.status = CodecStatus::MiddleOfLine;
+                    buf.push(b'.');
+                }
+                (_, CodecStatus::StartOfNewLine) => {
+                    self.status = CodecStatus::MiddleOfLine;
+                }
+                _ => {}
             }
         }
     }
 }
 
+#[derive(Debug, Copy, Clone)]
+#[allow(clippy::enum_variant_names)]
+enum CodecStatus {
+    /// We are past the first character of the current line
+    MiddleOfLine,
+    /// We just read a `\r` character
+    StartingNewLine,
+    /// We are at the start of a new line
+    StartOfNewLine,
+}
+
 /// Returns the string replacing all the CRLF with "\<CRLF\>"
 /// Used for debug displays
 #[cfg(feature = "tracing")]
@@ -113,9 +132,10 @@ mod test {
 
     #[test]
     fn test_codec() {
+        let mut buf = Vec::new();
         let mut codec = ClientCodec::new();
-        let mut buf: Vec<u8> = vec![];
 
+        codec.encode(b".\r\n", &mut buf);
         codec.encode(b"test\r\n", &mut buf);
         codec.encode(b"test\r\n\r\n", &mut buf);
         codec.encode(b".\r\n", &mut buf);
@@ -126,9 +146,13 @@ mod test {
         codec.encode(b"test\n", &mut buf);
         codec.encode(b".test\n", &mut buf);
         codec.encode(b"test", &mut buf);
+        codec.encode(b"test", &mut buf);
+        codec.encode(b"test\r\n", &mut buf);
+        codec.encode(b".test\r\n", &mut buf);
+        codec.encode(b"test.\r\n", &mut buf);
         assert_eq!(
             String::from_utf8(buf).unwrap(),
-            "test\r\ntest\r\n\r\n..\r\n\r\ntestte\r\n..\r\nsttesttest.test\n.test\ntest"
+            "..\r\ntest\r\ntest\r\n\r\n..\r\n\r\ntestte\r\n..\r\nsttesttest.test\n.test\ntesttesttest\r\n..test\r\ntest.\r\n"
         );
     }
 

src/transport/smtp/client/net.rs

@@ -1,23 +1,28 @@
+#[cfg(feature = "rustls-tls")]
+use std::sync::Arc;
 use std::{
     io::{self, Read, Write},
-    mem,
-    net::{Ipv4Addr, Shutdown, SocketAddr, SocketAddrV4, TcpStream, ToSocketAddrs},
+    net::{IpAddr, Shutdown, SocketAddr, TcpStream, ToSocketAddrs},
     time::Duration,
 };
 
+#[cfg(feature = "boring-tls")]
+use boring::ssl::SslStream;
 #[cfg(feature = "native-tls")]
 use native_tls::TlsStream;
 #[cfg(feature = "rustls-tls")]
-use rustls::{ClientConnection, ServerName, StreamOwned};
+use rustls::{pki_types::ServerName, ClientConnection, StreamOwned};
+use socket2::{Domain, Protocol, Type};
 
-#[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
 use super::InnerTlsParameters;
-use super::TlsParameters;
+use super::{ConnectionState, TlsParameters};
 use crate::transport::smtp::{error, Error};
 
 /// A network stream
 pub struct NetworkStream {
     inner: InnerNetworkStream,
+    state: ConnectionState,
 }
 
 /// Represents the different types of underlying network streams
@@ -33,49 +38,51 @@ enum InnerNetworkStream {
     /// Encrypted TCP stream
     #[cfg(feature = "rustls-tls")]
     RustlsTls(StreamOwned<ClientConnection, TcpStream>),
-    /// Can't be built
-    None,
+    #[cfg(feature = "boring-tls")]
+    BoringTls(SslStream<TcpStream>),
 }
 
 impl NetworkStream {
     fn new(inner: InnerNetworkStream) -> Self {
-        if let InnerNetworkStream::None = inner {
-            debug_assert!(false, "InnerNetworkStream::None must never be built");
+        NetworkStream {
+            inner,
+            state: ConnectionState::Ok,
         }
+    }
 
-        NetworkStream { inner }
+    pub(super) fn state(&self) -> ConnectionState {
+        self.state
+    }
+
+    pub(super) fn set_state(&mut self, state: ConnectionState) {
+        self.state = state;
     }
 
     /// Returns peer's address
     pub fn peer_addr(&self) -> io::Result<SocketAddr> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref s) => s.peer_addr(),
+        match &self.inner {
+            InnerNetworkStream::Tcp(s) => s.peer_addr(),
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref s) => s.get_ref().peer_addr(),
+            InnerNetworkStream::NativeTls(s) => s.get_ref().peer_addr(),
             #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref s) => s.get_ref().peer_addr(),
-            InnerNetworkStream::None => {
-                debug_assert!(false, "InnerNetworkStream::None must never be built");
-                Ok(SocketAddr::V4(SocketAddrV4::new(
-                    Ipv4Addr::new(127, 0, 0, 1),
-                    80,
-                )))
-            }
+            InnerNetworkStream::RustlsTls(s) => s.get_ref().peer_addr(),
+            #[cfg(feature = "boring-tls")]
+            InnerNetworkStream::BoringTls(s) => s.get_ref().peer_addr(),
         }
     }
 
     /// Shutdowns the connection
-    pub fn shutdown(&self, how: Shutdown) -> io::Result<()> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref s) => s.shutdown(how),
+    pub fn shutdown(&mut self, how: Shutdown) -> io::Result<()> {
+        self.state = ConnectionState::Closed;
+
+        match &self.inner {
+            InnerNetworkStream::Tcp(s) => s.shutdown(how),
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref s) => s.get_ref().shutdown(how),
+            InnerNetworkStream::NativeTls(s) => s.get_ref().shutdown(how),
             #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref s) => s.get_ref().shutdown(how),
-            InnerNetworkStream::None => {
-                debug_assert!(false, "InnerNetworkStream::None must never be built");
-                Ok(())
-            }
+            InnerNetworkStream::RustlsTls(s) => s.get_ref().shutdown(how),
+            #[cfg(feature = "boring-tls")]
+            InnerNetworkStream::BoringTls(s) => s.get_ref().shutdown(how),
         }
     }
 
@@ -83,19 +90,39 @@ impl NetworkStream {
         server: T,
         timeout: Option<Duration>,
         tls_parameters: Option<&TlsParameters>,
+        local_addr: Option<IpAddr>,
     ) -> Result<NetworkStream, Error> {
-        fn try_connect_timeout<T: ToSocketAddrs>(
+        fn try_connect<T: ToSocketAddrs>(
             server: T,
-            timeout: Duration,
+            timeout: Option<Duration>,
+            local_addr: Option<IpAddr>,
         ) -> Result<TcpStream, Error> {
-            let addrs = server.to_socket_addrs().map_err(error::connection)?;
+            let addrs = server
+                .to_socket_addrs()
+                .map_err(error::connection)?
+                .filter(|resolved_addr| resolved_address_filter(resolved_addr, local_addr));
 
             let mut last_err = None;
 
             for addr in addrs {
-                match TcpStream::connect_timeout(&addr, timeout) {
-                    Ok(stream) => return Ok(stream),
-                    Err(err) => last_err = Some(err),
+                let socket = socket2::Socket::new(
+                    Domain::for_address(addr),
+                    Type::STREAM,
+                    Some(Protocol::TCP),
+                )
+                .map_err(error::connection)?;
+                bind_local_address(&socket, &addr, local_addr)?;
+
+                if let Some(timeout) = timeout {
+                    match socket.connect_timeout(&addr.into(), timeout) {
+                        Ok(_) => return Ok(socket.into()),
+                        Err(err) => last_err = Some(err),
+                    }
+                } else {
+                    match socket.connect(&addr.into()) {
+                        Ok(_) => return Ok(socket.into()),
+                        Err(err) => last_err = Some(err),
+                    }
                 }
             }
 
@@ -105,43 +132,39 @@ impl NetworkStream {
             })
         }
 
-        let tcp_stream = match timeout {
-            Some(t) => try_connect_timeout(server, t)?,
-            None => TcpStream::connect(server).map_err(error::connection)?,
-        };
-
+        let tcp_stream = try_connect(server, timeout, local_addr)?;
         let mut stream = NetworkStream::new(InnerNetworkStream::Tcp(tcp_stream));
         if let Some(tls_parameters) = tls_parameters {
-            stream.upgrade_tls(tls_parameters)?;
+            stream = stream.upgrade_tls(tls_parameters)?;
         }
         Ok(stream)
     }
 
-    pub fn upgrade_tls(&mut self, tls_parameters: &TlsParameters) -> Result<(), Error> {
-        match &self.inner {
-            #[cfg(not(any(feature = "native-tls", feature = "rustls-tls")))]
+    pub fn upgrade_tls(self, tls_parameters: &TlsParameters) -> Result<Self, Error> {
+        match self.inner {
+            #[cfg(not(any(
+                feature = "native-tls",
+                feature = "rustls-tls",
+                feature = "boring-tls"
+            )))]
             InnerNetworkStream::Tcp(_) => {
                 let _ = tls_parameters;
                 panic!("Trying to upgrade an NetworkStream without having enabled either the native-tls or the rustls-tls feature");
             }
 
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
-            InnerNetworkStream::Tcp(_) => {
-                // get owned TcpStream
-                let tcp_stream = mem::replace(&mut self.inner, InnerNetworkStream::None);
-                let tcp_stream = match tcp_stream {
-                    InnerNetworkStream::Tcp(tcp_stream) => tcp_stream,
-                    _ => unreachable!(),
-                };
-
-                self.inner = Self::upgrade_tls_impl(tcp_stream, tls_parameters)?;
-                Ok(())
+            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+            InnerNetworkStream::Tcp(tcp_stream) => {
+                let inner = Self::upgrade_tls_impl(tcp_stream, tls_parameters)?;
+                Ok(Self {
+                    inner,
+                    state: ConnectionState::Ok,
+                })
             }
-            _ => Ok(()),
+            _ => Ok(self),
         }
     }
 
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
     fn upgrade_tls_impl(
         tcp_stream: TcpStream,
         tls_parameters: &TlsParameters,
@@ -158,29 +181,37 @@ impl NetworkStream {
             InnerTlsParameters::RustlsTls(connector) => {
                 let domain = ServerName::try_from(tls_parameters.domain())
                     .map_err(|_| error::connection("domain isn't a valid DNS name"))?;
-                let connection =
-                    ClientConnection::new(connector.clone(), domain).map_err(error::connection)?;
+                let connection = ClientConnection::new(Arc::clone(connector), domain.to_owned())
+                    .map_err(error::connection)?;
                 let stream = StreamOwned::new(connection, tcp_stream);
                 InnerNetworkStream::RustlsTls(stream)
             }
+            #[cfg(feature = "boring-tls")]
+            InnerTlsParameters::BoringTls(connector) => {
+                let stream = connector
+                    .configure()
+                    .map_err(error::connection)?
+                    .verify_hostname(tls_parameters.accept_invalid_hostnames)
+                    .connect(tls_parameters.domain(), tcp_stream)
+                    .map_err(error::connection)?;
+                InnerNetworkStream::BoringTls(stream)
+            }
         })
     }
 
     pub fn is_encrypted(&self) -> bool {
-        match self.inner {
+        match &self.inner {
             InnerNetworkStream::Tcp(_) => false,
             #[cfg(feature = "native-tls")]
             InnerNetworkStream::NativeTls(_) => true,
             #[cfg(feature = "rustls-tls")]
             InnerNetworkStream::RustlsTls(_) => true,
-            InnerNetworkStream::None => {
-                debug_assert!(false, "InnerNetworkStream::None must never be built");
-                false
-            }
+            #[cfg(feature = "boring-tls")]
+            InnerNetworkStream::BoringTls(_) => true,
         }
     }
 
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
     pub fn peer_certificate(&self) -> Result<Vec<u8>, Error> {
         match &self.inner {
             InnerNetworkStream::Tcp(_) => Err(error::client("Connection is not encrypted")),
@@ -198,94 +229,124 @@ impl NetworkStream {
                 .unwrap()
                 .first()
                 .unwrap()
-                .clone()
-                .0),
-            InnerNetworkStream::None => panic!("InnerNetworkStream::None must never be built"),
+                .to_vec()),
+            #[cfg(feature = "boring-tls")]
+            InnerNetworkStream::BoringTls(stream) => Ok(stream
+                .ssl()
+                .peer_certificate()
+                .unwrap()
+                .to_der()
+                .map_err(error::tls)?),
         }
     }
 
     pub fn set_read_timeout(&mut self, duration: Option<Duration>) -> io::Result<()> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref mut stream) => stream.set_read_timeout(duration),
+        match &mut self.inner {
+            InnerNetworkStream::Tcp(stream) => stream.set_read_timeout(duration),
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref mut stream) => {
-                stream.get_ref().set_read_timeout(duration)
-            }
+            InnerNetworkStream::NativeTls(stream) => stream.get_ref().set_read_timeout(duration),
             #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut stream) => {
-                stream.get_ref().set_read_timeout(duration)
-            }
-            InnerNetworkStream::None => {
-                debug_assert!(false, "InnerNetworkStream::None must never be built");
-                Ok(())
-            }
+            InnerNetworkStream::RustlsTls(stream) => stream.get_ref().set_read_timeout(duration),
+            #[cfg(feature = "boring-tls")]
+            InnerNetworkStream::BoringTls(stream) => stream.get_ref().set_read_timeout(duration),
         }
     }
 
     /// Set write timeout for IO calls
     pub fn set_write_timeout(&mut self, duration: Option<Duration>) -> io::Result<()> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref mut stream) => stream.set_write_timeout(duration),
+        match &mut self.inner {
+            InnerNetworkStream::Tcp(stream) => stream.set_write_timeout(duration),
 
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref mut stream) => {
-                stream.get_ref().set_write_timeout(duration)
-            }
+            InnerNetworkStream::NativeTls(stream) => stream.get_ref().set_write_timeout(duration),
             #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut stream) => {
-                stream.get_ref().set_write_timeout(duration)
-            }
-
-            InnerNetworkStream::None => {
-                debug_assert!(false, "InnerNetworkStream::None must never be built");
-                Ok(())
-            }
+            InnerNetworkStream::RustlsTls(stream) => stream.get_ref().set_write_timeout(duration),
+            #[cfg(feature = "boring-tls")]
+            InnerNetworkStream::BoringTls(stream) => stream.get_ref().set_write_timeout(duration),
         }
     }
 }
 
 impl Read for NetworkStream {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref mut s) => s.read(buf),
+        match &mut self.inner {
+            InnerNetworkStream::Tcp(s) => s.read(buf),
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref mut s) => s.read(buf),
+            InnerNetworkStream::NativeTls(s) => s.read(buf),
             #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut s) => s.read(buf),
-            InnerNetworkStream::None => {
-                debug_assert!(false, "InnerNetworkStream::None must never be built");
-                Ok(0)
-            }
+            InnerNetworkStream::RustlsTls(s) => s.read(buf),
+            #[cfg(feature = "boring-tls")]
+            InnerNetworkStream::BoringTls(s) => s.read(buf),
         }
     }
 }
 
 impl Write for NetworkStream {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref mut s) => s.write(buf),
+        match &mut self.inner {
+            InnerNetworkStream::Tcp(s) => s.write(buf),
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref mut s) => s.write(buf),
+            InnerNetworkStream::NativeTls(s) => s.write(buf),
             #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut s) => s.write(buf),
-            InnerNetworkStream::None => {
-                debug_assert!(false, "InnerNetworkStream::None must never be built");
-                Ok(0)
-            }
+            InnerNetworkStream::RustlsTls(s) => s.write(buf),
+            #[cfg(feature = "boring-tls")]
+            InnerNetworkStream::BoringTls(s) => s.write(buf),
         }
     }
 
     fn flush(&mut self) -> io::Result<()> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref mut s) => s.flush(),
+        match &mut self.inner {
+            InnerNetworkStream::Tcp(s) => s.flush(),
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref mut s) => s.flush(),
+            InnerNetworkStream::NativeTls(s) => s.flush(),
             #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut s) => s.flush(),
-            InnerNetworkStream::None => {
-                debug_assert!(false, "InnerNetworkStream::None must never be built");
-                Ok(())
-            }
+            InnerNetworkStream::RustlsTls(s) => s.flush(),
+            #[cfg(feature = "boring-tls")]
+            InnerNetworkStream::BoringTls(s) => s.flush(),
         }
     }
 }
+
+/// If the local address is set, binds the socket to this address.
+/// If local address is not set, then destination address is required to determine the default
+/// local address on some platforms.
+/// See: https://github.com/hyperium/hyper/blob/faf24c6ad8eee1c3d5ccc9a4d4835717b8e2903f/src/client/connect/http.rs#L560
+fn bind_local_address(
+    socket: &socket2::Socket,
+    dst_addr: &SocketAddr,
+    local_addr: Option<IpAddr>,
+) -> Result<(), Error> {
+    match local_addr {
+        Some(local_addr) => {
+            socket
+                .bind(&SocketAddr::new(local_addr, 0).into())
+                .map_err(error::connection)?;
+        }
+        _ => {
+            if cfg!(windows) {
+                // Windows requires a socket be bound before calling connect
+                let any: SocketAddr = match dst_addr {
+                    SocketAddr::V4(_) => ([0, 0, 0, 0], 0).into(),
+                    SocketAddr::V6(_) => ([0, 0, 0, 0, 0, 0, 0, 0], 0).into(),
+                };
+                socket.bind(&any.into()).map_err(error::connection)?;
+            }
+        }
+    }
+    Ok(())
+}
+
+/// When we have an iterator of resolved remote addresses, we must filter them to be the same
+/// protocol as the local address binding. If no local address is set, then all will be matched.
+pub(crate) fn resolved_address_filter(
+    resolved_addr: &SocketAddr,
+    local_addr: Option<IpAddr>,
+) -> bool {
+    match local_addr {
+        Some(local_addr) => match resolved_addr.ip() {
+            IpAddr::V4(_) => local_addr.is_ipv4(),
+            IpAddr::V6(_) => local_addr.is_ipv6(),
+        },
+        None => true,
+    }
+}

src/transport/smtp/client/tls.rs

@@ -1,23 +1,60 @@
 use std::fmt::{self, Debug};
 #[cfg(feature = "rustls-tls")]
-use std::{sync::Arc, time::SystemTime};
+use std::{io, sync::Arc};
 
+#[cfg(feature = "boring-tls")]
+use boring::{
+    ssl::{SslConnector, SslVersion},
+    x509::store::X509StoreBuilder,
+};
 #[cfg(feature = "native-tls")]
 use native_tls::{Protocol, TlsConnector};
 #[cfg(feature = "rustls-tls")]
 use rustls::{
-    client::{ServerCertVerified, ServerCertVerifier, WebPkiVerifier},
-    ClientConfig, Error as TlsError, OwnedTrustAnchor, RootCertStore, ServerName,
+    client::danger::{HandshakeSignatureValid, ServerCertVerified, ServerCertVerifier},
+    crypto::{verify_tls12_signature, verify_tls13_signature},
+    pki_types::{CertificateDer, ServerName, UnixTime},
+    ClientConfig, DigitallySignedStruct, Error as TlsError, RootCertStore, SignatureScheme,
 };
 
-#[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
 use crate::transport::smtp::{error, Error};
 
-/// Accepted protocols by default.
-/// This removes TLS 1.0 and 1.1 compared to tls-native defaults.
-// This is also rustls' default behavior
-#[cfg(feature = "native-tls")]
-const DEFAULT_TLS_MIN_PROTOCOL: Protocol = Protocol::Tlsv12;
+/// TLS protocol versions.
+#[derive(Debug, Copy, Clone)]
+#[non_exhaustive]
+#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+pub enum TlsVersion {
+    /// TLS 1.0
+    ///
+    /// Should only be used when trying to support legacy
+    /// SMTP servers that haven't updated to
+    /// at least TLS 1.2 yet.
+    ///
+    /// Supported by `native-tls` and `boring-tls`.
+    Tlsv10,
+    /// TLS 1.1
+    ///
+    /// Should only be used when trying to support legacy
+    /// SMTP servers that haven't updated to
+    /// at least TLS 1.2 yet.
+    ///
+    /// Supported by `native-tls` and `boring-tls`.
+    Tlsv11,
+    /// TLS 1.2
+    ///
+    /// A good option for most SMTP servers.
+    ///
+    /// Supported by all TLS backends.
+    Tlsv12,
+    /// TLS 1.3
+    ///
+    /// The most secure option, although not supported by all SMTP servers.
+    ///
+    /// Although it is technically supported by all TLS backends,
+    /// trying to set it for `native-tls` will give a runtime error.
+    Tlsv13,
+}
 
 /// How to apply TLS to a client connection
 #[derive(Clone)]
@@ -26,16 +63,25 @@ pub enum Tls {
     /// Insecure connection only (for testing purposes)
     None,
     /// Start with insecure connection and use `STARTTLS` when available
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
-    #[cfg_attr(docsrs, doc(cfg(any(feature = "native-tls", feature = "rustls-tls"))))]
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+    )]
     Opportunistic(TlsParameters),
     /// Start with insecure connection and require `STARTTLS`
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
-    #[cfg_attr(docsrs, doc(cfg(any(feature = "native-tls", feature = "rustls-tls"))))]
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+    )]
     Required(TlsParameters),
     /// Use TLS wrapped connection
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
-    #[cfg_attr(docsrs, doc(cfg(any(feature = "native-tls", feature = "rustls-tls"))))]
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+    )]
     Wrapper(TlsParameters),
 }
 
@@ -43,31 +89,60 @@ impl Debug for Tls {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match &self {
             Self::None => f.pad("None"),
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
             Self::Opportunistic(_) => f.pad("Opportunistic"),
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
             Self::Required(_) => f.pad("Required"),
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
             Self::Wrapper(_) => f.pad("Wrapper"),
         }
     }
 }
 
+/// Source for the base set of root certificates to trust.
+#[allow(missing_copy_implementations)]
+#[derive(Clone, Debug, Default)]
+pub enum CertificateStore {
+    /// Use the default for the TLS backend.
+    ///
+    /// For native-tls, this will use the system certificate store on Windows, the keychain on
+    /// macOS, and OpenSSL directories on Linux (usually `/etc/ssl`).
+    ///
+    /// For rustls, this will also use the the system store if the `rustls-native-certs` feature is
+    /// enabled, or will fall back to `webpki-roots`.
+    ///
+    /// The boring-tls backend uses the same logic as OpenSSL on all platforms.
+    #[default]
+    Default,
+    /// Use a hardcoded set of Mozilla roots via the `webpki-roots` crate.
+    ///
+    /// This option is only available in the rustls backend.
+    #[cfg(feature = "rustls-tls")]
+    WebpkiRoots,
+    /// Don't use any system certificates.
+    None,
+}
+
 /// Parameters to use for secure clients
 #[derive(Clone)]
 pub struct TlsParameters {
     pub(crate) connector: InnerTlsParameters,
     /// The domain name which is expected in the TLS certificate from the server
     pub(super) domain: String,
+    #[cfg(feature = "boring-tls")]
+    pub(super) accept_invalid_hostnames: bool,
 }
 
 /// Builder for `TlsParameters`
 #[derive(Debug, Clone)]
 pub struct TlsParametersBuilder {
     domain: String,
+    cert_store: CertificateStore,
     root_certs: Vec<Certificate>,
     accept_invalid_hostnames: bool,
     accept_invalid_certs: bool,
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    min_tls_version: TlsVersion,
 }
 
 impl TlsParametersBuilder {
@@ -75,12 +150,21 @@ impl TlsParametersBuilder {
     pub fn new(domain: String) -> Self {
         Self {
             domain,
+            cert_store: CertificateStore::Default,
             root_certs: Vec::new(),
             accept_invalid_hostnames: false,
             accept_invalid_certs: false,
+            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+            min_tls_version: TlsVersion::Tlsv12,
         }
     }
 
+    /// Set the source for the base set of root certificates to trust.
+    pub fn certificate_store(mut self, cert_store: CertificateStore) -> Self {
+        self.cert_store = cert_store;
+        self
+    }
+
     /// Add a custom root certificate
     ///
     /// Can be used to safely connect to a server using a self signed certificate, for example.
@@ -102,13 +186,22 @@ impl TlsParametersBuilder {
     /// This method introduces significant vulnerabilities to man-in-the-middle attacks.
     ///
     /// Hostname verification can only be disabled with the `native-tls` TLS backend.
-    #[cfg(feature = "native-tls")]
-    #[cfg_attr(docsrs, doc(cfg(feature = "native-tls")))]
+    #[cfg(any(feature = "native-tls", feature = "boring-tls"))]
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "native-tls", feature = "boring-tls"))))]
     pub fn dangerous_accept_invalid_hostnames(mut self, accept_invalid_hostnames: bool) -> Self {
         self.accept_invalid_hostnames = accept_invalid_hostnames;
         self
     }
 
+    /// Controls which minimum TLS version is allowed
+    ///
+    /// Defaults to [`Tlsv12`][TlsVersion::Tlsv12].
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    pub fn set_min_tls_version(mut self, min_tls_version: TlsVersion) -> Self {
+        self.min_tls_version = min_tls_version;
+        self
+    }
+
     /// Controls whether invalid certificates are accepted
     ///
     /// Defaults to `false`.
@@ -130,16 +223,20 @@ impl TlsParametersBuilder {
         self
     }
 
-    /// Creates a new `TlsParameters` using native-tls or rustls
+    /// Creates a new `TlsParameters` using native-tls, boring-tls or rustls
     /// depending on which one is available
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
-    #[cfg_attr(docsrs, doc(cfg(any(feature = "native-tls", feature = "rustls-tls"))))]
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+    )]
     pub fn build(self) -> Result<TlsParameters, Error> {
         #[cfg(feature = "rustls-tls")]
         return self.build_rustls();
-
-        #[cfg(not(feature = "rustls-tls"))]
+        #[cfg(all(not(feature = "rustls-tls"), feature = "native-tls"))]
         return self.build_native();
+        #[cfg(all(not(feature = "rustls-tls"), feature = "boring-tls"))]
+        return self.build_boring();
     }
 
     /// Creates a new `TlsParameters` using native-tls with the provided configuration
@@ -148,17 +245,93 @@ impl TlsParametersBuilder {
     pub fn build_native(self) -> Result<TlsParameters, Error> {
         let mut tls_builder = TlsConnector::builder();
 
+        match self.cert_store {
+            CertificateStore::Default => {}
+            CertificateStore::None => {
+                tls_builder.disable_built_in_roots(true);
+            }
+            #[allow(unreachable_patterns)]
+            other => {
+                return Err(error::tls(format!(
+                    "{other:?} is not supported in native tls"
+                )))
+            }
+        }
         for cert in self.root_certs {
             tls_builder.add_root_certificate(cert.native_tls);
         }
         tls_builder.danger_accept_invalid_hostnames(self.accept_invalid_hostnames);
         tls_builder.danger_accept_invalid_certs(self.accept_invalid_certs);
 
-        tls_builder.min_protocol_version(Some(DEFAULT_TLS_MIN_PROTOCOL));
+        let min_tls_version = match self.min_tls_version {
+            TlsVersion::Tlsv10 => Protocol::Tlsv10,
+            TlsVersion::Tlsv11 => Protocol::Tlsv11,
+            TlsVersion::Tlsv12 => Protocol::Tlsv12,
+            TlsVersion::Tlsv13 => {
+                return Err(error::tls(
+                    "min tls version Tlsv13 not supported in native tls",
+                ))
+            }
+        };
+
+        tls_builder.min_protocol_version(Some(min_tls_version));
         let connector = tls_builder.build().map_err(error::tls)?;
         Ok(TlsParameters {
             connector: InnerTlsParameters::NativeTls(connector),
             domain: self.domain,
+            #[cfg(feature = "boring-tls")]
+            accept_invalid_hostnames: self.accept_invalid_hostnames,
+        })
+    }
+
+    /// Creates a new `TlsParameters` using boring-tls with the provided configuration
+    #[cfg(feature = "boring-tls")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "boring-tls")))]
+    pub fn build_boring(self) -> Result<TlsParameters, Error> {
+        use boring::ssl::{SslMethod, SslVerifyMode};
+
+        let mut tls_builder = SslConnector::builder(SslMethod::tls_client()).map_err(error::tls)?;
+
+        if self.accept_invalid_certs {
+            tls_builder.set_verify(SslVerifyMode::NONE);
+        } else {
+            match self.cert_store {
+                CertificateStore::Default => {}
+                CertificateStore::None => {
+                    // Replace the default store with an empty store.
+                    tls_builder
+                        .set_cert_store(X509StoreBuilder::new().map_err(error::tls)?.build());
+                }
+                #[allow(unreachable_patterns)]
+                other => {
+                    return Err(error::tls(format!(
+                        "{other:?} is not supported in boring tls"
+                    )))
+                }
+            }
+
+            let cert_store = tls_builder.cert_store_mut();
+
+            for cert in self.root_certs {
+                cert_store.add_cert(cert.boring_tls).map_err(error::tls)?;
+            }
+        }
+
+        let min_tls_version = match self.min_tls_version {
+            TlsVersion::Tlsv10 => SslVersion::TLS1,
+            TlsVersion::Tlsv11 => SslVersion::TLS1_1,
+            TlsVersion::Tlsv12 => SslVersion::TLS1_2,
+            TlsVersion::Tlsv13 => SslVersion::TLS1_3,
+        };
+
+        tls_builder
+            .set_min_proto_version(Some(min_tls_version))
+            .map_err(error::tls)?;
+        let connector = tls_builder.build();
+        Ok(TlsParameters {
+            connector: InnerTlsParameters::BoringTls(connector),
+            domain: self.domain,
+            accept_invalid_hostnames: self.accept_invalid_hostnames,
         })
     }
 
@@ -166,59 +339,98 @@ impl TlsParametersBuilder {
     #[cfg(feature = "rustls-tls")]
     #[cfg_attr(docsrs, doc(cfg(feature = "rustls-tls")))]
     pub fn build_rustls(self) -> Result<TlsParameters, Error> {
-        let tls = ClientConfig::builder();
-        let tls = tls.with_safe_defaults();
+        let just_version3 = &[&rustls::version::TLS13];
+        let supported_versions = match self.min_tls_version {
+            TlsVersion::Tlsv10 => {
+                return Err(error::tls("min tls version Tlsv10 not supported in rustls"))
+            }
+            TlsVersion::Tlsv11 => {
+                return Err(error::tls("min tls version Tlsv11 not supported in rustls"))
+            }
+            TlsVersion::Tlsv12 => rustls::ALL_VERSIONS,
+            TlsVersion::Tlsv13 => just_version3,
+        };
+
+        let tls = ClientConfig::builder_with_protocol_versions(supported_versions);
 
         let tls = if self.accept_invalid_certs {
-            tls.with_custom_certificate_verifier(Arc::new(InvalidCertsVerifier {}))
+            tls.dangerous()
+                .with_custom_certificate_verifier(Arc::new(InvalidCertsVerifier {}))
         } else {
             let mut root_cert_store = RootCertStore::empty();
+
+            #[cfg(feature = "rustls-native-certs")]
+            fn load_native_roots(store: &mut RootCertStore) -> Result<(), Error> {
+                let native_certs = rustls_native_certs::load_native_certs().map_err(error::tls)?;
+                let (added, ignored) = store.add_parsable_certificates(native_certs);
+                #[cfg(feature = "tracing")]
+                tracing::debug!(
+                    "loaded platform certs with {added} valid and {ignored} ignored (invalid) certs"
+                );
+                Ok(())
+            }
+
+            #[cfg(feature = "rustls-tls")]
+            fn load_webpki_roots(store: &mut RootCertStore) {
+                store.extend(webpki_roots::TLS_SERVER_ROOTS.iter().cloned());
+            }
+
+            match self.cert_store {
+                CertificateStore::Default => {
+                    #[cfg(feature = "rustls-native-certs")]
+                    load_native_roots(&mut root_cert_store)?;
+                    #[cfg(not(feature = "rustls-native-certs"))]
+                    load_webpki_roots(&mut root_cert_store);
+                }
+                #[cfg(feature = "rustls-tls")]
+                CertificateStore::WebpkiRoots => {
+                    load_webpki_roots(&mut root_cert_store);
+                }
+                CertificateStore::None => {}
+            }
             for cert in self.root_certs {
                 for rustls_cert in cert.rustls {
-                    root_cert_store.add(&rustls_cert).map_err(error::tls)?;
+                    root_cert_store.add(rustls_cert).map_err(error::tls)?;
                 }
             }
-            root_cert_store.add_server_trust_anchors(webpki_roots::TLS_SERVER_ROOTS.0.iter().map(
-                |ta| {
-                    OwnedTrustAnchor::from_subject_spki_name_constraints(
-                        ta.subject,
-                        ta.spki,
-                        ta.name_constraints,
-                    )
-                },
-            ));
 
-            tls.with_custom_certificate_verifier(Arc::new(WebPkiVerifier::new(
-                root_cert_store,
-                None,
-            )))
+            tls.with_root_certificates(root_cert_store)
         };
         let tls = tls.with_no_client_auth();
 
         Ok(TlsParameters {
             connector: InnerTlsParameters::RustlsTls(Arc::new(tls)),
             domain: self.domain,
+            #[cfg(feature = "boring-tls")]
+            accept_invalid_hostnames: self.accept_invalid_hostnames,
         })
     }
 }
 
 #[derive(Clone)]
+#[allow(clippy::enum_variant_names)]
 pub enum InnerTlsParameters {
     #[cfg(feature = "native-tls")]
     NativeTls(TlsConnector),
     #[cfg(feature = "rustls-tls")]
     RustlsTls(Arc<ClientConfig>),
+    #[cfg(feature = "boring-tls")]
+    BoringTls(SslConnector),
 }
 
 impl TlsParameters {
     /// Creates a new `TlsParameters` using native-tls or rustls
     /// depending on which one is available
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
-    #[cfg_attr(docsrs, doc(cfg(any(feature = "native-tls", feature = "rustls-tls"))))]
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+    )]
     pub fn new(domain: String) -> Result<Self, Error> {
         TlsParametersBuilder::new(domain).build()
     }
 
+    /// Creates a new `TlsParameters` builder
     pub fn builder(domain: String) -> TlsParametersBuilder {
         TlsParametersBuilder::new(domain)
     }
@@ -237,6 +449,13 @@ impl TlsParameters {
         TlsParametersBuilder::new(domain).build_rustls()
     }
 
+    /// Creates a new `TlsParameters` using boring
+    #[cfg(feature = "boring-tls")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "boring-tls")))]
+    pub fn new_boring(domain: String) -> Result<Self, Error> {
+        TlsParametersBuilder::new(domain).build_boring()
+    }
+
     pub fn domain(&self) -> &str {
         &self.domain
     }
@@ -249,21 +468,28 @@ pub struct Certificate {
     #[cfg(feature = "native-tls")]
     native_tls: native_tls::Certificate,
     #[cfg(feature = "rustls-tls")]
-    rustls: Vec<rustls::Certificate>,
+    rustls: Vec<CertificateDer<'static>>,
+    #[cfg(feature = "boring-tls")]
+    boring_tls: boring::x509::X509,
 }
 
-#[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
 impl Certificate {
     /// Create a `Certificate` from a DER encoded certificate
     pub fn from_der(der: Vec<u8>) -> Result<Self, Error> {
         #[cfg(feature = "native-tls")]
         let native_tls_cert = native_tls::Certificate::from_der(&der).map_err(error::tls)?;
 
+        #[cfg(feature = "boring-tls")]
+        let boring_tls_cert = boring::x509::X509::from_der(&der).map_err(error::tls)?;
+
         Ok(Self {
             #[cfg(feature = "native-tls")]
             native_tls: native_tls_cert,
             #[cfg(feature = "rustls-tls")]
-            rustls: vec![rustls::Certificate(der)],
+            rustls: vec![der.into()],
+            #[cfg(feature = "boring-tls")]
+            boring_tls: boring_tls_cert,
         })
     }
 
@@ -272,16 +498,17 @@ impl Certificate {
         #[cfg(feature = "native-tls")]
         let native_tls_cert = native_tls::Certificate::from_pem(pem).map_err(error::tls)?;
 
+        #[cfg(feature = "boring-tls")]
+        let boring_tls_cert = boring::x509::X509::from_pem(pem).map_err(error::tls)?;
+
         #[cfg(feature = "rustls-tls")]
         let rustls_cert = {
             use std::io::Cursor;
 
             let mut pem = Cursor::new(pem);
             rustls_pemfile::certs(&mut pem)
+                .collect::<io::Result<Vec<_>>>()
                 .map_err(|_| error::tls("invalid certificates"))?
-                .into_iter()
-                .map(rustls::Certificate)
-                .collect::<Vec<_>>()
         };
 
         Ok(Self {
@@ -289,6 +516,8 @@ impl Certificate {
             native_tls: native_tls_cert,
             #[cfg(feature = "rustls-tls")]
             rustls: rustls_cert,
+            #[cfg(feature = "boring-tls")]
+            boring_tls: boring_tls_cert,
         })
     }
 }
@@ -300,19 +529,53 @@ impl Debug for Certificate {
 }
 
 #[cfg(feature = "rustls-tls")]
+#[derive(Debug)]
 struct InvalidCertsVerifier;
 
 #[cfg(feature = "rustls-tls")]
 impl ServerCertVerifier for InvalidCertsVerifier {
     fn verify_server_cert(
         &self,
-        _end_entity: &rustls::Certificate,
-        _intermediates: &[rustls::Certificate],
-        _server_name: &ServerName,
-        _scts: &mut dyn Iterator<Item = &[u8]>,
+        _end_entity: &CertificateDer<'_>,
+        _intermediates: &[CertificateDer<'_>],
+        _server_name: &ServerName<'_>,
         _ocsp_response: &[u8],
-        _now: SystemTime,
+        _now: UnixTime,
     ) -> Result<ServerCertVerified, TlsError> {
         Ok(ServerCertVerified::assertion())
     }
+
+    fn verify_tls12_signature(
+        &self,
+        message: &[u8],
+        cert: &CertificateDer<'_>,
+        dss: &DigitallySignedStruct,
+    ) -> Result<HandshakeSignatureValid, TlsError> {
+        verify_tls12_signature(
+            message,
+            cert,
+            dss,
+            &rustls::crypto::ring::default_provider().signature_verification_algorithms,
+        )
+    }
+
+    fn verify_tls13_signature(
+        &self,
+        message: &[u8],
+        cert: &CertificateDer<'_>,
+        dss: &DigitallySignedStruct,
+    ) -> Result<HandshakeSignatureValid, TlsError> {
+        verify_tls13_signature(
+            message,
+            cert,
+            dss,
+            &rustls::crypto::ring::default_provider().signature_verification_algorithms,
+        )
+    }
+
+    fn supported_verify_schemes(&self) -> Vec<SignatureScheme> {
+        rustls::crypto::ring::default_provider()
+            .signature_verification_algorithms
+            .supported_schemes()
+    }
 }

src/transport/smtp/commands.rs

@@ -13,7 +13,7 @@ use crate::{
 };
 
 /// EHLO command
-#[derive(PartialEq, Clone, Debug)]
+#[derive(PartialEq, Eq, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Ehlo {
     client_id: ClientId,
@@ -33,7 +33,7 @@ impl Ehlo {
 }
 
 /// STARTTLS command
-#[derive(PartialEq, Clone, Debug, Copy)]
+#[derive(PartialEq, Eq, Clone, Debug, Copy)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Starttls;
 
@@ -44,7 +44,7 @@ impl Display for Starttls {
 }
 
 /// MAIL command
-#[derive(PartialEq, Clone, Debug)]
+#[derive(PartialEq, Eq, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Mail {
     sender: Option<Address>,
@@ -59,7 +59,7 @@ impl Display for Mail {
             self.sender.as_ref().map_or("", |s| s.as_ref())
         )?;
         for parameter in &self.parameters {
-            write!(f, " {}", parameter)?;
+            write!(f, " {parameter}")?;
         }
         f.write_str("\r\n")
     }
@@ -73,7 +73,7 @@ impl Mail {
 }
 
 /// RCPT command
-#[derive(PartialEq, Clone, Debug)]
+#[derive(PartialEq, Eq, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Rcpt {
     recipient: Address,
@@ -84,7 +84,7 @@ impl Display for Rcpt {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         write!(f, "RCPT TO:<{}>", self.recipient)?;
         for parameter in &self.parameters {
-            write!(f, " {}", parameter)?;
+            write!(f, " {parameter}")?;
         }
         f.write_str("\r\n")
     }
@@ -101,7 +101,7 @@ impl Rcpt {
 }
 
 /// DATA command
-#[derive(PartialEq, Clone, Debug, Copy)]
+#[derive(PartialEq, Eq, Clone, Debug, Copy)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Data;
 
@@ -112,7 +112,7 @@ impl Display for Data {
 }
 
 /// QUIT command
-#[derive(PartialEq, Clone, Debug, Copy)]
+#[derive(PartialEq, Eq, Clone, Debug, Copy)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Quit;
 
@@ -123,7 +123,7 @@ impl Display for Quit {
 }
 
 /// NOOP command
-#[derive(PartialEq, Clone, Debug, Copy)]
+#[derive(PartialEq, Eq, Clone, Debug, Copy)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Noop;
 
@@ -134,7 +134,7 @@ impl Display for Noop {
 }
 
 /// HELP command
-#[derive(PartialEq, Clone, Debug)]
+#[derive(PartialEq, Eq, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Help {
     argument: Option<String>,
@@ -144,7 +144,7 @@ impl Display for Help {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         f.write_str("HELP")?;
         if let Some(argument) = &self.argument {
-            write!(f, " {}", argument)?;
+            write!(f, " {argument}")?;
         }
         f.write_str("\r\n")
     }
@@ -158,7 +158,7 @@ impl Help {
 }
 
 /// VRFY command
-#[derive(PartialEq, Clone, Debug)]
+#[derive(PartialEq, Eq, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Vrfy {
     argument: String,
@@ -178,7 +178,7 @@ impl Vrfy {
 }
 
 /// EXPN command
-#[derive(PartialEq, Clone, Debug)]
+#[derive(PartialEq, Eq, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Expn {
     argument: String,
@@ -198,7 +198,7 @@ impl Expn {
 }
 
 /// RSET command
-#[derive(PartialEq, Clone, Debug, Copy)]
+#[derive(PartialEq, Eq, Clone, Debug, Copy)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Rset;
 
@@ -209,7 +209,7 @@ impl Display for Rset {
 }
 
 /// AUTH command
-#[derive(PartialEq, Clone, Debug)]
+#[derive(PartialEq, Eq, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Auth {
     mechanism: Mechanism,
@@ -220,7 +220,7 @@ pub struct Auth {
 
 impl Display for Auth {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        let encoded_response = self.response.as_ref().map(base64::encode);
+        let encoded_response = self.response.as_ref().map(crate::base64::encode);
 
         if self.mechanism.supports_initial_response() {
             write!(f, "AUTH {} {}", self.mechanism, encoded_response.unwrap())?;
@@ -271,7 +271,7 @@ impl Auth {
         #[cfg(feature = "tracing")]
         tracing::debug!("auth encoded challenge: {}", encoded_challenge);
 
-        let decoded_base64 = base64::decode(&encoded_challenge).map_err(error::response)?;
+        let decoded_base64 = crate::base64::decode(encoded_challenge).map_err(error::response)?;
         let decoded_challenge = String::from_utf8(decoded_base64).map_err(error::response)?;
         #[cfg(feature = "tracing")]
         tracing::debug!("auth decoded challenge: {}", decoded_challenge);
@@ -296,15 +296,15 @@ mod test {
 
     #[test]
     fn test_display() {
-        let id = ClientId::Domain("localhost".to_string());
+        let id = ClientId::Domain("localhost".to_owned());
         let email = Address::from_str("test@example.com").unwrap();
         let mail_parameter = MailParameter::Other {
-            keyword: "TEST".to_string(),
-            value: Some("value".to_string()),
+            keyword: "TEST".to_owned(),
+            value: Some("value".to_owned()),
         };
         let rcpt_parameter = RcptParameter::Other {
-            keyword: "TEST".to_string(),
-            value: Some("value".to_string()),
+            keyword: "TEST".to_owned(),
+            value: Some("value".to_owned()),
         };
         assert_eq!(format!("{}", Ehlo::new(id)), "EHLO localhost\r\n");
         assert_eq!(
@@ -341,24 +341,18 @@ mod test {
             format!("{}", Rcpt::new(email, vec![rcpt_parameter])),
             "RCPT TO:<test@example.com> TEST=value\r\n"
         );
-        assert_eq!(format!("{}", Quit), "QUIT\r\n");
-        assert_eq!(format!("{}", Data), "DATA\r\n");
-        assert_eq!(format!("{}", Noop), "NOOP\r\n");
+        assert_eq!(format!("{Quit}"), "QUIT\r\n");
+        assert_eq!(format!("{Data}"), "DATA\r\n");
+        assert_eq!(format!("{Noop}"), "NOOP\r\n");
         assert_eq!(format!("{}", Help::new(None)), "HELP\r\n");
         assert_eq!(
-            format!("{}", Help::new(Some("test".to_string()))),
+            format!("{}", Help::new(Some("test".to_owned()))),
             "HELP test\r\n"
         );
-        assert_eq!(
-            format!("{}", Vrfy::new("test".to_string())),
-            "VRFY test\r\n"
-        );
-        assert_eq!(
-            format!("{}", Expn::new("test".to_string())),
-            "EXPN test\r\n"
-        );
-        assert_eq!(format!("{}", Rset), "RSET\r\n");
-        let credentials = Credentials::new("user".to_string(), "password".to_string());
+        assert_eq!(format!("{}", Vrfy::new("test".to_owned())), "VRFY test\r\n");
+        assert_eq!(format!("{}", Expn::new("test".to_owned())), "EXPN test\r\n");
+        assert_eq!(format!("{Rset}"), "RSET\r\n");
+        let credentials = Credentials::new("user".to_owned(), "password".to_owned());
         assert_eq!(
             format!(
                 "{}",

src/transport/smtp/connection_url.rs

@@ -0,0 +1,129 @@
+use url::Url;
+
+#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+use super::client::{Tls, TlsParameters};
+#[cfg(any(feature = "tokio1", feature = "async-std1"))]
+use super::AsyncSmtpTransportBuilder;
+use super::{
+    authentication::Credentials, error, extension::ClientId, Error, SmtpTransportBuilder,
+    SMTP_PORT, SUBMISSIONS_PORT, SUBMISSION_PORT,
+};
+
+pub(crate) trait TransportBuilder {
+    fn new<T: Into<String>>(server: T) -> Self;
+    fn tls(self, tls: super::Tls) -> Self;
+    fn port(self, port: u16) -> Self;
+    fn credentials(self, credentials: Credentials) -> Self;
+    fn hello_name(self, name: ClientId) -> Self;
+}
+
+impl TransportBuilder for SmtpTransportBuilder {
+    fn new<T: Into<String>>(server: T) -> Self {
+        Self::new(server)
+    }
+
+    fn tls(self, tls: super::Tls) -> Self {
+        self.tls(tls)
+    }
+
+    fn port(self, port: u16) -> Self {
+        self.port(port)
+    }
+
+    fn credentials(self, credentials: Credentials) -> Self {
+        self.credentials(credentials)
+    }
+
+    fn hello_name(self, name: ClientId) -> Self {
+        self.hello_name(name)
+    }
+}
+
+#[cfg(any(feature = "tokio1", feature = "async-std1"))]
+impl TransportBuilder for AsyncSmtpTransportBuilder {
+    fn new<T: Into<String>>(server: T) -> Self {
+        Self::new(server)
+    }
+
+    fn tls(self, tls: super::Tls) -> Self {
+        self.tls(tls)
+    }
+
+    fn port(self, port: u16) -> Self {
+        self.port(port)
+    }
+
+    fn credentials(self, credentials: Credentials) -> Self {
+        self.credentials(credentials)
+    }
+
+    fn hello_name(self, name: ClientId) -> Self {
+        self.hello_name(name)
+    }
+}
+
+/// Create a new SmtpTransportBuilder or AsyncSmtpTransportBuilder from a connection URL
+pub(crate) fn from_connection_url<B: TransportBuilder>(connection_url: &str) -> Result<B, Error> {
+    let connection_url = Url::parse(connection_url).map_err(error::connection)?;
+    let tls: Option<String> = connection_url
+        .query_pairs()
+        .find(|(k, _)| k == "tls")
+        .map(|(_, v)| v.to_string());
+
+    let host = connection_url
+        .host_str()
+        .ok_or_else(|| error::connection("smtp host undefined"))?;
+
+    let mut builder = B::new(host);
+
+    match (connection_url.scheme(), tls.as_deref()) {
+        ("smtp", None) => {
+            builder = builder.port(connection_url.port().unwrap_or(SMTP_PORT));
+        }
+        #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+        ("smtp", Some("required")) => {
+            builder = builder
+                .port(connection_url.port().unwrap_or(SUBMISSION_PORT))
+                .tls(Tls::Required(TlsParameters::new(host.into())?))
+        }
+        #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+        ("smtp", Some("opportunistic")) => {
+            builder = builder
+                .port(connection_url.port().unwrap_or(SUBMISSION_PORT))
+                .tls(Tls::Opportunistic(TlsParameters::new(host.into())?))
+        }
+        #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+        ("smtps", _) => {
+            builder = builder
+                .port(connection_url.port().unwrap_or(SUBMISSIONS_PORT))
+                .tls(Tls::Wrapper(TlsParameters::new(host.into())?))
+        }
+        (scheme, tls) => {
+            return Err(error::connection(format!(
+                "Unknown scheme '{scheme}' or tls parameter '{tls:?}', note that a transport with TLS requires one of the TLS features"
+            )))
+        }
+    };
+
+    // use the path segment of the URL as name in the name in the HELO / EHLO command
+    if connection_url.path().len() > 1 {
+        let name = connection_url.path().trim_matches('/').to_owned();
+        builder = builder.hello_name(ClientId::Domain(name));
+    }
+
+    if let Some(password) = connection_url.password() {
+        let percent_decode = |s: &str| {
+            percent_encoding::percent_decode_str(s)
+                .decode_utf8()
+                .map(|cow| cow.into_owned())
+                .map_err(error::connection)
+        };
+        let credentials = Credentials::new(
+            percent_decode(connection_url.username())?,
+            percent_decode(password)?,
+        );
+        builder = builder.credentials(credentials);
+    }
+
+    Ok(builder)
+}

src/transport/smtp/error.rs

@@ -68,8 +68,11 @@ impl Error {
     }
 
     /// Returns true if the error is from TLS
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
-    #[cfg_attr(docsrs, doc(cfg(any(feature = "native-tls", feature = "rustls-tls"))))]
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+    )]
     pub fn is_tls(&self) -> bool {
         matches!(self.inner.kind, Kind::Tls)
     }
@@ -102,8 +105,11 @@ pub(crate) enum Kind {
     /// Underlying network i/o error
     Network,
     /// TLS error
-    #[cfg_attr(docsrs, doc(cfg(any(feature = "native-tls", feature = "rustls-tls"))))]
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+    )]
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
     Tls,
 }
 
@@ -113,7 +119,7 @@ impl fmt::Debug for Error {
 
         builder.field("kind", &self.inner.kind);
 
-        if let Some(ref source) = self.inner.source {
+        if let Some(source) = &self.inner.source {
             builder.field("source", source);
         }
 
@@ -123,23 +129,23 @@ impl fmt::Debug for Error {
 
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self.inner.kind {
+        match &self.inner.kind {
             Kind::Response => f.write_str("response error")?,
             Kind::Client => f.write_str("internal client error")?,
             Kind::Network => f.write_str("network error")?,
             Kind::Connection => f.write_str("Connection error")?,
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
             Kind::Tls => f.write_str("tls error")?,
-            Kind::Transient(ref code) => {
-                write!(f, "transient error ({})", code)?;
+            Kind::Transient(code) => {
+                write!(f, "transient error ({code})")?;
             }
-            Kind::Permanent(ref code) => {
-                write!(f, "permanent error ({})", code)?;
+            Kind::Permanent(code) => {
+                write!(f, "permanent error ({code})")?;
             }
         };
 
-        if let Some(ref e) = self.inner.source {
-            write!(f, ": {}", e)?;
+        if let Some(e) = &self.inner.source {
+            write!(f, ": {e}")?;
         }
 
         Ok(())
@@ -179,7 +185,7 @@ pub(crate) fn connection<E: Into<BoxError>>(e: E) -> Error {
     Error::new(Kind::Connection, Some(e))
 }
 
-#[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
 pub(crate) fn tls<E: Into<BoxError>>(e: E) -> Error {
     Error::new(Kind::Tls, Some(e))
 }

src/transport/smtp/extension.rs

@@ -4,7 +4,6 @@ use std::{
     collections::HashSet,
     fmt::{self, Display, Formatter},
     net::{Ipv4Addr, Ipv6Addr},
-    result::Result,
 };
 
 use crate::transport::smtp::{
@@ -53,10 +52,10 @@ impl Default for ClientId {
 
 impl Display for ClientId {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        match *self {
-            Self::Domain(ref value) => f.write_str(value),
-            Self::Ipv4(ref value) => write!(f, "[{}]", value),
-            Self::Ipv6(ref value) => write!(f, "[IPv6:{}]", value),
+        match self {
+            Self::Domain(value) => f.write_str(value),
+            Self::Ipv4(value) => write!(f, "[{value}]"),
+            Self::Ipv6(value) => write!(f, "[IPv6:{value}]"),
         }
     }
 }
@@ -93,11 +92,11 @@ pub enum Extension {
 
 impl Display for Extension {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        match *self {
+        match self {
             Extension::EightBitMime => f.write_str("8BITMIME"),
             Extension::SmtpUtfEight => f.write_str("SMTPUTF8"),
             Extension::StartTls => f.write_str("STARTTLS"),
-            Extension::Authentication(ref mechanism) => write!(f, "AUTH {}", mechanism),
+            Extension::Authentication(mechanism) => write!(f, "AUTH {mechanism}"),
         }
     }
 }
@@ -119,7 +118,7 @@ pub struct ServerInfo {
 impl Display for ServerInfo {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         let features = if self.features.is_empty() {
-            "no supported features".to_string()
+            "no supported features".to_owned()
         } else {
             format!("{:?}", self.features)
         };
@@ -174,7 +173,7 @@ impl ServerInfo {
         }
 
         Ok(ServerInfo {
-            name: name.to_string(),
+            name: name.to_owned(),
             features,
         })
     }
@@ -190,7 +189,7 @@ impl ServerInfo {
             .contains(&Extension::Authentication(mechanism))
     }
 
-    /// Gets a compatible mechanism from list
+    /// Gets a compatible mechanism from a list
     pub fn get_auth_mechanism(&self, mechanisms: &[Mechanism]) -> Option<Mechanism> {
         for mechanism in mechanisms {
             if self.supports_auth_mechanism(*mechanism) {
@@ -227,16 +226,16 @@ pub enum MailParameter {
 
 impl Display for MailParameter {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        match *self {
-            MailParameter::Body(ref value) => write!(f, "BODY={}", value),
-            MailParameter::Size(size) => write!(f, "SIZE={}", size),
+        match self {
+            MailParameter::Body(value) => write!(f, "BODY={value}"),
+            MailParameter::Size(size) => write!(f, "SIZE={size}"),
             MailParameter::SmtpUtfEight => f.write_str("SMTPUTF8"),
             MailParameter::Other {
-                ref keyword,
-                value: Some(ref value),
+                keyword,
+                value: Some(value),
             } => write!(f, "{}={}", keyword, XText(value)),
             MailParameter::Other {
-                ref keyword,
+                keyword,
                 value: None,
             } => f.write_str(keyword),
         }
@@ -277,13 +276,13 @@ pub enum RcptParameter {
 
 impl Display for RcptParameter {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        match *self {
+        match &self {
             RcptParameter::Other {
-                ref keyword,
-                value: Some(ref value),
-            } => write!(f, "{}={}", keyword, XText(value)),
+                keyword,
+                value: Some(value),
+            } => write!(f, "{keyword}={}", XText(value)),
             RcptParameter::Other {
-                ref keyword,
+                keyword,
                 value: None,
             } => f.write_str(keyword),
         }
@@ -304,21 +303,21 @@ mod test {
     #[test]
     fn test_clientid_fmt() {
         assert_eq!(
-            format!("{}", ClientId::Domain("test".to_string())),
-            "test".to_string()
+            format!("{}", ClientId::Domain("test".to_owned())),
+            "test".to_owned()
         );
-        assert_eq!(format!("{}", LOCALHOST_CLIENT), "[127.0.0.1]".to_string());
+        assert_eq!(format!("{LOCALHOST_CLIENT}"), "[127.0.0.1]".to_owned());
     }
 
     #[test]
     fn test_extension_fmt() {
         assert_eq!(
             format!("{}", Extension::EightBitMime),
-            "8BITMIME".to_string()
+            "8BITMIME".to_owned()
         );
         assert_eq!(
             format!("{}", Extension::Authentication(Mechanism::Plain)),
-            "AUTH PLAIN".to_string()
+            "AUTH PLAIN".to_owned()
         );
     }
 
@@ -331,11 +330,11 @@ mod test {
             format!(
                 "{}",
                 ServerInfo {
-                    name: "name".to_string(),
+                    name: "name".to_owned(),
                     features: eightbitmime,
                 }
             ),
-            "name with {EightBitMime}".to_string()
+            "name with {EightBitMime}".to_owned()
         );
 
         let empty = HashSet::new();
@@ -344,11 +343,11 @@ mod test {
             format!(
                 "{}",
                 ServerInfo {
-                    name: "name".to_string(),
+                    name: "name".to_owned(),
                     features: empty,
                 }
             ),
-            "name with no supported features".to_string()
+            "name with no supported features".to_owned()
         );
 
         let mut plain = HashSet::new();
@@ -358,11 +357,11 @@ mod test {
             format!(
                 "{}",
                 ServerInfo {
-                    name: "name".to_string(),
+                    name: "name".to_owned(),
                     features: plain,
                 }
             ),
-            "name with {Authentication(Plain)}".to_string()
+            "name with {Authentication(Plain)}".to_owned()
         );
     }
 
@@ -374,18 +373,14 @@ mod test {
                 Category::Unspecified4,
                 Detail::One,
             ),
-            vec![
-                "me".to_string(),
-                "8BITMIME".to_string(),
-                "SIZE 42".to_string(),
-            ],
+            vec!["me".to_owned(), "8BITMIME".to_owned(), "SIZE 42".to_owned()],
         );
 
         let mut features = HashSet::new();
         assert!(features.insert(Extension::EightBitMime));
 
         let server_info = ServerInfo {
-            name: "me".to_string(),
+            name: "me".to_owned(),
             features,
         };
 
@@ -401,10 +396,10 @@ mod test {
                 Detail::One,
             ),
             vec![
-                "me".to_string(),
-                "AUTH PLAIN CRAM-MD5 XOAUTH2 OTHER".to_string(),
-                "8BITMIME".to_string(),
-                "SIZE 42".to_string(),
+                "me".to_owned(),
+                "AUTH PLAIN CRAM-MD5 XOAUTH2 OTHER".to_owned(),
+                "8BITMIME".to_owned(),
+                "SIZE 42".to_owned(),
             ],
         );
 
@@ -414,7 +409,7 @@ mod test {
         assert!(features2.insert(Extension::Authentication(Mechanism::Xoauth2),));
 
         let server_info2 = ServerInfo {
-            name: "me".to_string(),
+            name: "me".to_owned(),
             features: features2,
         };
 

src/transport/smtp/mod.rs

@@ -77,8 +77,8 @@
 //! let sender = SmtpTransport::starttls_relay("smtp.example.com")?
 //!     // Add credentials for authentication
 //!     .credentials(Credentials::new(
-//!         "username".to_string(),
-//!         "password".to_string(),
+//!         "username".to_owned(),
+//!         "password".to_owned(),
 //!     ))
 //!     // Configure expected authentication mechanism
 //!     .authentication(vec![Mechanism::Plain])
@@ -111,7 +111,7 @@
 //!     .body(String::from("Be happy!"))?;
 //!
 //! // Custom TLS configuration
-//! let tls = TlsParameters::builder("smtp.example.com".to_string())
+//! let tls = TlsParameters::builder("smtp.example.com".to_owned())
 //!     .dangerous_accept_invalid_certs(true)
 //!     .build()?;
 //!
@@ -140,7 +140,7 @@ pub use self::{
     error::Error,
     transport::{SmtpTransport, SmtpTransportBuilder},
 };
-#[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
 use crate::transport::smtp::client::TlsParameters;
 use crate::transport::smtp::{
     authentication::{Credentials, Mechanism, DEFAULT_MECHANISMS},
@@ -154,6 +154,7 @@ mod async_transport;
 pub mod authentication;
 pub mod client;
 pub mod commands;
+mod connection_url;
 mod error;
 pub mod extension;
 #[cfg(feature = "pool")]
@@ -200,7 +201,7 @@ struct SmtpInfo {
 impl Default for SmtpInfo {
     fn default() -> Self {
         Self {
-            server: "localhost".to_string(),
+            server: "localhost".to_owned(),
             port: SMTP_PORT,
             hello_name: ClientId::default(),
             credentials: None,

src/transport/smtp/pool/async_impl.rs

@@ -2,7 +2,7 @@ use std::{
     fmt::{self, Debug},
     mem,
     ops::{Deref, DerefMut},
-    sync::Arc,
+    sync::{Arc, OnceLock},
     time::{Duration, Instant},
 };
 
@@ -10,7 +10,6 @@ use futures_util::{
     lock::Mutex,
     stream::{self, StreamExt},
 };
-use once_cell::sync::OnceCell;
 
 use super::{
     super::{client::AsyncSmtpConnection, Error},
@@ -22,7 +21,7 @@ pub struct Pool<E: Executor> {
     config: PoolConfig,
     connections: Mutex<Vec<ParkedConnection>>,
     client: AsyncSmtpClient<E>,
-    handle: OnceCell<E::Handle>,
+    handle: OnceLock<E::Handle>,
 }
 
 struct ParkedConnection {
@@ -41,7 +40,7 @@ impl<E: Executor> Pool<E> {
             config,
             connections: Mutex::new(Vec::new()),
             client,
-            handle: OnceCell::new(),
+            handle: OnceLock::new(),
         });
 
         {
@@ -158,14 +157,14 @@ impl<E: Executor> Pool<E> {
                     #[cfg(feature = "tracing")]
                     tracing::debug!("reusing a pooled connection");
 
-                    return Ok(PooledConnection::wrap(conn, self.clone()));
+                    return Ok(PooledConnection::wrap(conn, Arc::clone(self)));
                 }
                 None => {
                     #[cfg(feature = "tracing")]
                     tracing::debug!("creating a new connection");
 
                     let conn = self.client.connection().await?;
-                    return Ok(PooledConnection::wrap(conn, self.clone()));
+                    return Ok(PooledConnection::wrap(conn, Arc::clone(self)));
                 }
             }
         }
@@ -203,7 +202,7 @@ impl<E: Executor> Debug for Pool<E> {
                 &match self.connections.try_lock() {
                     Some(connections) => format!("{} connections", connections.len()),
 
-                    None => "LOCKED".to_string(),
+                    None => "LOCKED".to_owned(),
                 },
             )
             .field("client", &self.client)

src/transport/smtp/pool/sync_impl.rs

@@ -141,14 +141,14 @@ impl Pool {
                     #[cfg(feature = "tracing")]
                     tracing::debug!("reusing a pooled connection");
 
-                    return Ok(PooledConnection::wrap(conn, self.clone()));
+                    return Ok(PooledConnection::wrap(conn, Arc::clone(self)));
                 }
                 None => {
                     #[cfg(feature = "tracing")]
                     tracing::debug!("creating a new connection");
 
                     let conn = self.client.connection()?;
-                    return Ok(PooledConnection::wrap(conn, self.clone()));
+                    return Ok(PooledConnection::wrap(conn, Arc::clone(self)));
                 }
             }
         }
@@ -186,8 +186,8 @@ impl Debug for Pool {
                 &match self.connections.try_lock() {
                     Ok(connections) => format!("{} connections", connections.len()),
 
-                    Err(TryLockError::WouldBlock) => "LOCKED".to_string(),
-                    Err(TryLockError::Poisoned(_)) => "POISONED".to_string(),
+                    Err(TryLockError::WouldBlock) => "LOCKED".to_owned(),
+                    Err(TryLockError::Poisoned(_)) => "POISONED".to_owned(),
                 },
             )
             .field("client", &self.client)

src/transport/smtp/response.rs

@@ -5,7 +5,6 @@ use std::{
     fmt::{Display, Formatter, Result},
     result,
     str::FromStr,
-    string::ToString,
 };
 
 use nom::{
@@ -19,7 +18,7 @@ use nom::{
 
 use crate::transport::smtp::{error, Error};
 
-/// First digit indicates severity
+/// The first digit indicates severity
 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub enum Severity {
@@ -132,6 +131,12 @@ impl Code {
     }
 }
 
+impl From<Code> for u16 {
+    fn from(code: Code) -> Self {
+        code.detail as u16 + 10 * code.category as u16 + 100 * code.severity as u16
+    }
+}
+
 /// Contains an SMTP reply, with separated code and message
 ///
 /// The text message is optional, only the code is mandatory
@@ -151,7 +156,7 @@ impl FromStr for Response {
     fn from_str(s: &str) -> result::Result<Response, Error> {
         parse_response(s)
             .map(|(_, r)| r)
-            .map_err(|e| error::response(e.to_string()))
+            .map_err(|e| error::response(e.to_owned()))
     }
 }
 
@@ -317,6 +322,17 @@ mod test {
         assert_eq!(code.to_string(), "421");
     }
 
+    #[test]
+    fn test_code_to_u16() {
+        let code = Code {
+            severity: Severity::TransientNegativeCompletion,
+            category: Category::Connections,
+            detail: Detail::One,
+        };
+        let c: u16 = code.into();
+        assert_eq!(c, 421);
+    }
+
     #[test]
     fn test_response_from_str() {
         let raw_response = "250-me\r\n250-8BITMIME\r\n250-SIZE 42\r\n250 AUTH PLAIN CRAM-MD5\r\n";
@@ -329,10 +345,10 @@ mod test {
                     detail: Detail::Zero,
                 },
                 message: vec![
-                    "me".to_string(),
-                    "8BITMIME".to_string(),
-                    "SIZE 42".to_string(),
-                    "AUTH PLAIN CRAM-MD5".to_string(),
+                    "me".to_owned(),
+                    "8BITMIME".to_owned(),
+                    "SIZE 42".to_owned(),
+                    "AUTH PLAIN CRAM-MD5".to_owned(),
                 ],
             }
         );
@@ -352,11 +368,7 @@ mod test {
                 category: Category::MailSystem,
                 detail: Detail::Zero,
             },
-            vec![
-                "me".to_string(),
-                "8BITMIME".to_string(),
-                "SIZE 42".to_string(),
-            ],
+            vec!["me".to_owned(), "8BITMIME".to_owned(), "SIZE 42".to_owned(),],
         )
         .is_positive());
         assert!(!Response::new(
@@ -365,11 +377,7 @@ mod test {
                 category: Category::MailSystem,
                 detail: Detail::Zero,
             },
-            vec![
-                "me".to_string(),
-                "8BITMIME".to_string(),
-                "SIZE 42".to_string(),
-            ],
+            vec!["me".to_owned(), "8BITMIME".to_owned(), "SIZE 42".to_owned(),],
         )
         .is_positive());
     }
@@ -382,11 +390,7 @@ mod test {
                 category: Category::MailSystem,
                 detail: Detail::One,
             },
-            vec![
-                "me".to_string(),
-                "8BITMIME".to_string(),
-                "SIZE 42".to_string(),
-            ],
+            vec!["me".to_owned(), "8BITMIME".to_owned(), "SIZE 42".to_owned(),],
         )
         .has_code(451));
         assert!(!Response::new(
@@ -395,11 +399,7 @@ mod test {
                 category: Category::MailSystem,
                 detail: Detail::One,
             },
-            vec![
-                "me".to_string(),
-                "8BITMIME".to_string(),
-                "SIZE 42".to_string(),
-            ],
+            vec!["me".to_owned(), "8BITMIME".to_owned(), "SIZE 42".to_owned(),],
         )
         .has_code(251));
     }
@@ -413,11 +413,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec![
-                    "me".to_string(),
-                    "8BITMIME".to_string(),
-                    "SIZE 42".to_string(),
-                ],
+                vec!["me".to_owned(), "8BITMIME".to_owned(), "SIZE 42".to_owned(),],
             )
             .first_word(),
             Some("me")
@@ -430,9 +426,9 @@ mod test {
                     detail: Detail::One,
                 },
                 vec![
-                    "me mo".to_string(),
-                    "8BITMIME".to_string(),
-                    "SIZE 42".to_string(),
+                    "me mo".to_owned(),
+                    "8BITMIME".to_owned(),
+                    "SIZE 42".to_owned(),
                 ],
             )
             .first_word(),
@@ -457,7 +453,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec![" ".to_string()],
+                vec![" ".to_owned()],
             )
             .first_word(),
             None
@@ -469,7 +465,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec!["  ".to_string()],
+                vec!["  ".to_owned()],
             )
             .first_word(),
             None
@@ -481,7 +477,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec!["".to_string()],
+                vec!["".to_owned()],
             )
             .first_word(),
             None
@@ -494,7 +490,7 @@ mod test {
         let res = parse_response(raw_response);
         match res {
             Err(nom::Err::Incomplete(_)) => {}
-            _ => panic!("Expected incomplete response, got {:?}", res),
+            _ => panic!("Expected incomplete response, got {res:?}"),
         }
     }
 
@@ -507,11 +503,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec![
-                    "me".to_string(),
-                    "8BITMIME".to_string(),
-                    "SIZE 42".to_string(),
-                ],
+                vec!["me".to_owned(), "8BITMIME".to_owned(), "SIZE 42".to_owned(),],
             )
             .first_line(),
             Some("me")
@@ -524,9 +516,9 @@ mod test {
                     detail: Detail::One,
                 },
                 vec![
-                    "me mo".to_string(),
-                    "8BITMIME".to_string(),
-                    "SIZE 42".to_string(),
+                    "me mo".to_owned(),
+                    "8BITMIME".to_owned(),
+                    "SIZE 42".to_owned(),
                 ],
             )
             .first_line(),
@@ -551,7 +543,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec![" ".to_string()],
+                vec![" ".to_owned()],
             )
             .first_line(),
             Some(" ")
@@ -563,7 +555,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec!["  ".to_string()],
+                vec!["  ".to_owned()],
             )
             .first_line(),
             Some("  ")
@@ -575,7 +567,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec!["".to_string()],
+                vec!["".to_owned()],
             )
             .first_line(),
             Some("")

src/transport/smtp/transport.rs

@@ -1,13 +1,13 @@
 #[cfg(feature = "pool")]
 use std::sync::Arc;
-use std::time::Duration;
+use std::{fmt::Debug, time::Duration};
 
 #[cfg(feature = "pool")]
 use super::pool::sync_impl::Pool;
 #[cfg(feature = "pool")]
 use super::PoolConfig;
 use super::{ClientId, Credentials, Error, Mechanism, Response, SmtpConnection, SmtpInfo};
-#[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
 use super::{Tls, TlsParameters, SUBMISSIONS_PORT, SUBMISSION_PORT};
 use crate::{address::Envelope, Transport};
 
@@ -38,6 +38,14 @@ impl Transport for SmtpTransport {
     }
 }
 
+impl Debug for SmtpTransport {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let mut builder = f.debug_struct("SmtpTransport");
+        builder.field("inner", &self.inner);
+        builder.finish()
+    }
+}
+
 impl SmtpTransport {
     /// Simple and secure transport, using TLS connections to communicate with the SMTP server
     ///
@@ -45,8 +53,11 @@ impl SmtpTransport {
     ///
     /// Creates an encrypted transport over submissions port, using the provided domain
     /// to validate TLS certificates.
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
-    #[cfg_attr(docsrs, doc(cfg(any(feature = "native-tls", feature = "rustls-tls"))))]
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+    )]
     pub fn relay(relay: &str) -> Result<SmtpTransportBuilder, Error> {
         let tls_parameters = TlsParameters::new(relay.into())?;
 
@@ -55,7 +66,7 @@ impl SmtpTransport {
             .tls(Tls::Wrapper(tls_parameters)))
     }
 
-    /// Simple an secure transport, using STARTTLS to obtain encrypted connections
+    /// Simple and secure transport, using STARTTLS to obtain encrypted connections
     ///
     /// Alternative to [`SmtpTransport::relay`](#method.relay), for SMTP servers
     /// that don't take SMTPS connections.
@@ -66,8 +77,11 @@ impl SmtpTransport {
     ///
     /// An error is returned if the connection can't be upgraded. No credentials
     /// or emails will be sent to the server, protecting from downgrade attacks.
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
-    #[cfg_attr(docsrs, doc(cfg(any(feature = "native-tls", feature = "rustls-tls"))))]
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+    )]
     pub fn starttls_relay(relay: &str) -> Result<SmtpTransportBuilder, Error> {
         let tls_parameters = TlsParameters::new(relay.into())?;
 
@@ -89,29 +103,106 @@ impl SmtpTransport {
     ///
     /// * No authentication
     /// * No TLS
-    /// * A 60 seconds timeout for smtp commands
+    /// * A 60-seconds timeout for smtp commands
     /// * Port 25
     ///
     /// Consider using [`SmtpTransport::relay`](#method.relay) or
     /// [`SmtpTransport::starttls_relay`](#method.starttls_relay) instead,
     /// if possible.
     pub fn builder_dangerous<T: Into<String>>(server: T) -> SmtpTransportBuilder {
-        let new = SmtpInfo {
-            server: server.into(),
-            ..Default::default()
-        };
+        SmtpTransportBuilder::new(server)
+    }
 
-        SmtpTransportBuilder {
-            info: new,
-            #[cfg(feature = "pool")]
-            pool_config: PoolConfig::default(),
-        }
+    /// Creates a `SmtpTransportBuilder` from a connection URL
+    ///
+    /// The protocol, credentials, host and port can be provided in a single URL.
+    /// Use the scheme `smtp` for an unencrypted relay (optionally in combination with the
+    /// `tls` parameter to allow/require STARTTLS) or `smtps` for SMTP over TLS.
+    /// The path section of the url can be used to set an alternative name for
+    /// the HELO / EHLO command.
+    /// For example `smtps://username:password@smtp.example.com/client.example.com:465`
+    /// will set the HELO / EHLO name `client.example.com`.
+    ///
+    /// <table>
+    ///   <thead>
+    ///     <tr>
+    ///       <th>scheme</th>
+    ///       <th>tls parameter</th>
+    ///       <th>example</th>
+    ///       <th>remarks</th>
+    ///     </tr>
+    ///   </thead>
+    ///   <tbody>
+    ///     <tr>
+    ///      <td>smtps</td>
+    ///      <td>-</td>
+    ///      <td>smtps://smtp.example.com</td>
+    ///      <td>SMTP over TLS, recommended method</td>
+    ///     </tr>
+    ///     <tr>
+    ///      <td>smtp</td>
+    ///      <td>required</td>
+    ///      <td>smtp://smtp.example.com?tls=required</td>
+    ///      <td>SMTP with STARTTLS required, when SMTP over TLS is not available</td>
+    ///     </tr>
+    ///     <tr>
+    ///      <td>smtp</td>
+    ///      <td>opportunistic</td>
+    ///      <td>smtp://smtp.example.com?tls=opportunistic</td>
+    ///      <td>
+    ///         SMTP with optionally STARTTLS when supported by the server.
+    ///         Caution: this method is vulnerable to a man-in-the-middle attack.
+    ///         Not recommended for production use.
+    ///       </td>
+    ///     </tr>
+    ///     <tr>
+    ///      <td>smtp</td>
+    ///      <td>-</td>
+    ///      <td>smtp://smtp.example.com</td>
+    ///      <td>Unencrypted SMTP, not recommended for production use.</td>
+    ///     </tr>
+    ///   </tbody>
+    /// </table>
+    ///
+    /// ```rust,no_run
+    /// use lettre::{
+    ///     message::header::ContentType, transport::smtp::authentication::Credentials, Message,
+    ///     SmtpTransport, Transport,
+    /// };
+    ///
+    /// let email = Message::builder()
+    ///     .from("NoBody <nobody@domain.tld>".parse().unwrap())
+    ///     .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
+    ///     .to("Hei <hei@domain.tld>".parse().unwrap())
+    ///     .subject("Happy new year")
+    ///     .header(ContentType::TEXT_PLAIN)
+    ///     .body(String::from("Be happy!"))
+    ///     .unwrap();
+    ///
+    /// // Open a remote connection to example
+    /// let mailer = SmtpTransport::from_url("smtps://username:password@smtp.example.com:465")
+    ///     .unwrap()
+    ///     .build();
+    ///
+    /// // Send the email
+    /// match mailer.send(&email) {
+    ///     Ok(_) => println!("Email sent successfully!"),
+    ///     Err(e) => panic!("Could not send email: {e:?}"),
+    /// }
+    /// ```
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+    )]
+    pub fn from_url(connection_url: &str) -> Result<SmtpTransportBuilder, Error> {
+        super::connection_url::from_connection_url(connection_url)
     }
 
     /// Tests the SMTP connection
     ///
     /// `test_connection()` tests the connection by using the SMTP NOOP command.
-    /// The connection is closed afterwards if a connection pool is not used.
+    /// The connection is closed afterward if a connection pool is not used.
     pub fn test_connection(&self) -> Result<bool, Error> {
         let mut conn = self.inner.connection()?;
 
@@ -135,6 +226,20 @@ pub struct SmtpTransportBuilder {
 
 /// Builder for the SMTP `SmtpTransport`
 impl SmtpTransportBuilder {
+    // Create new builder with default parameters
+    pub(crate) fn new<T: Into<String>>(server: T) -> Self {
+        let new = SmtpInfo {
+            server: server.into(),
+            ..Default::default()
+        };
+
+        Self {
+            info: new,
+            #[cfg(feature = "pool")]
+            pool_config: PoolConfig::default(),
+        }
+    }
+
     /// Set the name used during EHLO
     pub fn hello_name(mut self, name: ClientId) -> Self {
         self.info.hello_name = name;
@@ -166,8 +271,11 @@ impl SmtpTransportBuilder {
     }
 
     /// Set the TLS settings to use
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
-    #[cfg_attr(docsrs, doc(cfg(any(feature = "native-tls", feature = "rustls-tls"))))]
+    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+    )]
     pub fn tls(mut self, tls: Tls) -> Self {
         self.info.tls = tls;
         self
@@ -185,7 +293,7 @@ impl SmtpTransportBuilder {
 
     /// Build the transport
     ///
-    /// If the `pool` feature is enabled an `Arc` wrapped pool is be created.
+    /// If the `pool` feature is enabled, an `Arc` wrapped pool is created.
     /// Defaults can be found at [`PoolConfig`]
     pub fn build(self) -> SmtpTransport {
         let client = SmtpClient { info: self.info };
@@ -209,9 +317,9 @@ impl SmtpClient {
     /// Handles encryption and authentication
     pub fn connection(&self) -> Result<SmtpConnection, Error> {
         #[allow(clippy::match_single_binding)]
-        let tls_parameters = match self.info.tls {
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
-            Tls::Wrapper(ref tls_parameters) => Some(tls_parameters),
+        let tls_parameters = match &self.info.tls {
+            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+            Tls::Wrapper(tls_parameters) => Some(tls_parameters),
             _ => None,
         };
 
@@ -221,17 +329,18 @@ impl SmtpClient {
             self.info.timeout,
             &self.info.hello_name,
             tls_parameters,
+            None,
         )?;
 
-        #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
-        match self.info.tls {
-            Tls::Opportunistic(ref tls_parameters) => {
+        #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+        match &self.info.tls {
+            Tls::Opportunistic(tls_parameters) => {
                 if conn.can_starttls() {
-                    conn.starttls(tls_parameters, &self.info.hello_name)?;
+                    conn = conn.starttls(tls_parameters, &self.info.hello_name)?;
                 }
             }
-            Tls::Required(ref tls_parameters) => {
-                conn.starttls(tls_parameters, &self.info.hello_name)?;
+            Tls::Required(tls_parameters) => {
+                conn = conn.starttls(tls_parameters, &self.info.hello_name)?;
             }
             _ => (),
         }
@@ -242,3 +351,78 @@ impl SmtpClient {
         Ok(conn)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        transport::smtp::{authentication::Credentials, client::Tls},
+        SmtpTransport,
+    };
+
+    #[test]
+    fn transport_from_url() {
+        let builder = SmtpTransport::from_url("smtp://127.0.0.1:2525").unwrap();
+
+        assert_eq!(builder.info.port, 2525);
+        assert!(matches!(builder.info.tls, Tls::None));
+        assert_eq!(builder.info.server, "127.0.0.1");
+
+        let builder =
+            SmtpTransport::from_url("smtps://username:password@smtp.example.com:465").unwrap();
+
+        assert_eq!(builder.info.port, 465);
+        assert_eq!(
+            builder.info.credentials,
+            Some(Credentials::new(
+                "username".to_owned(),
+                "password".to_owned()
+            ))
+        );
+        assert!(matches!(builder.info.tls, Tls::Wrapper(_)));
+        assert_eq!(builder.info.server, "smtp.example.com");
+
+        let builder = SmtpTransport::from_url(
+            "smtps://user%40example.com:pa$$word%3F%22!@smtp.example.com:465",
+        )
+        .unwrap();
+
+        assert_eq!(builder.info.port, 465);
+        assert_eq!(
+            builder.info.credentials,
+            Some(Credentials::new(
+                "user@example.com".to_owned(),
+                "pa$$word?\"!".to_owned()
+            ))
+        );
+        assert!(matches!(builder.info.tls, Tls::Wrapper(_)));
+        assert_eq!(builder.info.server, "smtp.example.com");
+
+        let builder =
+            SmtpTransport::from_url("smtp://username:password@smtp.example.com:587?tls=required")
+                .unwrap();
+
+        assert_eq!(builder.info.port, 587);
+        assert_eq!(
+            builder.info.credentials,
+            Some(Credentials::new(
+                "username".to_owned(),
+                "password".to_owned()
+            ))
+        );
+        assert!(matches!(builder.info.tls, Tls::Required(_)));
+
+        let builder = SmtpTransport::from_url(
+            "smtp://username:password@smtp.example.com:587?tls=opportunistic",
+        )
+        .unwrap();
+
+        assert_eq!(builder.info.port, 587);
+        assert!(matches!(builder.info.tls, Tls::Opportunistic(_)));
+
+        let builder = SmtpTransport::from_url("smtps://smtp.example.com").unwrap();
+
+        assert_eq!(builder.info.port, 465);
+        assert_eq!(builder.info.credentials, None);
+        assert!(matches!(builder.info.tls, Tls::Wrapper(_)));
+    }
+}

src/transport/smtp/util.rs

@@ -41,7 +41,7 @@ mod tests {
         ]
         .iter()
         {
-            assert_eq!(format!("{}", XText(input)), expect.to_string());
+            assert_eq!(format!("{}", XText(input)), (*expect).to_owned());
         }
     }
 }

src/transport/stub/mod.rs

@@ -53,6 +53,8 @@ use futures_util::lock::Mutex as FuturesMutex;
 use crate::AsyncTransport;
 use crate::{address::Envelope, Transport};
 
+/// An error returned by the stub transport
+#[non_exhaustive]
 #[derive(Debug, Copy, Clone)]
 pub struct Error;
 

testdata/email_with_png.eml

@@ -4,7 +4,7 @@ Reply-To: Yuin <yuin@domain.tld>
 To: Hei <hei@domain.tld>
 Subject: Happy new year
 MIME-Version: 1.0
-Content-Type: multipart/related; 
+Content-Type: multipart/related;
  boundary="GUEEoEeTXtLcK2sMhmH1RfC1co13g4rtnRUFjQFA"
 
 --0oVZ2r6AoLAhLlb0gPNSKy6BEqdS2IfwxrcbUuo1

tests/transport_file.rs

@@ -33,7 +33,7 @@ mod sync {
         let result = sender.send(&email);
         let id = result.unwrap();
 
-        let eml_file = temp_dir().join(format!("{}.eml", id));
+        let eml_file = temp_dir().join(format!("{id}.eml"));
         let eml = read_to_string(&eml_file).unwrap();
 
         assert_eq!(
@@ -68,10 +68,10 @@ mod sync {
         let result = sender.send(&email);
         let id = result.unwrap();
 
-        let eml_file = temp_dir().join(format!("{}.eml", id));
+        let eml_file = temp_dir().join(format!("{id}.eml"));
         let eml = read_to_string(&eml_file).unwrap();
 
-        let json_file = temp_dir().join(format!("{}.json", id));
+        let json_file = temp_dir().join(format!("{id}.json"));
         let json = read_to_string(&json_file).unwrap();
 
         assert_eq!(
@@ -131,7 +131,7 @@ mod tokio_1 {
         let result = sender.send(email).await;
         let id = result.unwrap();
 
-        let eml_file = temp_dir().join(format!("{}.eml", id));
+        let eml_file = temp_dir().join(format!("{id}.eml"));
         let eml = read_to_string(&eml_file).unwrap();
 
         assert_eq!(
@@ -182,7 +182,7 @@ mod asyncstd_1 {
         let result = sender.send(email).await;
         let id = result.unwrap();
 
-        let eml_file = temp_dir().join(format!("{}.eml", id));
+        let eml_file = temp_dir().join(format!("{id}.eml"));
         let eml = read_to_string(&eml_file).unwrap();
 
         assert_eq!(

tests/transport_sendmail.rs

@@ -15,7 +15,7 @@ mod sync {
             .unwrap();
 
         let result = sender.send(&email);
-        println!("{:?}", result);
+        println!("{result:?}");
         assert!(result.is_ok());
     }
 }
@@ -42,7 +42,7 @@ mod tokio_1 {
             .unwrap();
 
         let result = sender.send(email).await;
-        println!("{:?}", result);
+        println!("{result:?}");
         assert!(result.is_ok());
     }
 }
@@ -68,7 +68,7 @@ mod asyncstd_1 {
             .unwrap();
 
         let result = sender.send(email).await;
-        println!("{:?}", result);
+        println!("{result:?}");
         assert!(result.is_ok());
     }
 }

tests/transport_stub.rs

@@ -18,7 +18,7 @@ mod sync {
         sender_ok.send(&email).unwrap();
         sender_ko.send(&email).unwrap_err();
 
-        let expected_messages = vec![(
+        let expected_messages = [(
             email.envelope().clone(),
             String::from_utf8(email.formatted()).unwrap(),
         )];
@@ -47,7 +47,7 @@ mod tokio_1 {
         sender_ok.send(email.clone()).await.unwrap();
         sender_ko.send(email.clone()).await.unwrap_err();
 
-        let expected_messages = vec![(
+        let expected_messages = [(
             email.envelope().clone(),
             String::from_utf8(email.formatted()).unwrap(),
         )];
@@ -75,7 +75,7 @@ mod asyncstd_1 {
         sender_ok.send(email.clone()).await.unwrap();
         sender_ko.send(email.clone()).await.unwrap_err();
 
-        let expected_messages = vec![(
+        let expected_messages = [(
             email.envelope().clone(),
             String::from_utf8(email.formatted()).unwrap(),
         )];