fix

Bumps [tokio](https://github.com/tokio-rs/tokio) from 1.44.1 to 1.44.2.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](https://github.com/tokio-rs/tokio/compare/tokio-1.44.1...tokio-1.44.2)

---
updated-dependencies:
- dependency-name: tokio
  dependency-version: 1.44.2
  dependency-type: indirect
...

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

.github/workflows/test.yml

@@ -13,16 +13,16 @@ env:
 
 jobs:
   rustfmt:
-    name: rustfmt / nightly-2022-11-12
+    name: rustfmt / nightly-2024-09-01
     runs-on: ubuntu-latest
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Install rust
         run: |
-          rustup default nightly-2022-11-12
+          rustup default nightly-2024-09-01
           rustup component add rustfmt
 
       - name: cargo fmt
@@ -34,7 +34,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Install rust
         run: |
@@ -50,19 +50,19 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - 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
 
       - name: Check with cargo hack
-        run: cargo hack check --feature-powerset --depth 3
+        run: cargo hack check --feature-powerset --depth 3 --at-least-one-of aws-lc-rs,ring --at-least-one-of rustls-native-certs,webpki-roots
 
   test:
     name: test / ${{ matrix.name }}
@@ -75,12 +75,12 @@ jobs:
             rust: stable
           - name: beta
             rust: beta
-          - name: 1.60.0
-            rust: 1.60.0
+          - name: '1.74'
+            rust: '1.74'
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Install rust
         run: |
@@ -90,7 +90,7 @@ jobs:
       - name: Setup cache
         uses: Swatinem/rust-cache@v2
 
-      - name: Install postfix  
+      - name: Install postfix
         run: |
           DEBIAN_FRONTEND=noninteractive sudo apt-get update
           DEBIAN_FRONTEND=noninteractive sudo apt-get -y install postfix
@@ -112,9 +112,6 @@ jobs:
       - name: Install dkimverify
         run: sudo apt -y install python3-dkim
 
-      - name: Work around early dependencies MSRV bump
-        run: cargo update -p async-global-executor --precise 2.0.4
-
       - name: Test with no default features
         run: cargo test --no-default-features
 
@@ -122,16 +119,16 @@ jobs:
         run: cargo test
 
       - name: Test with all features (-native-tls)
-        run: cargo test --no-default-features --features async-std,async-std1,async-std1-rustls-tls,async-trait,base64,boring,boring-tls,builder,dkim,ed25519-dalek,email-encoding,fastrand,file-transport,file-transport-envelope,futures-io,futures-rustls,futures-util,hostname,httpdate,mime,mime03,nom,once_cell,pool,quoted_printable,rsa,rustls,rustls-pemfile,rustls-tls,sendmail-transport,serde,serde_json,sha2,smtp-transport,socket2,tokio1,tokio1-boring-tls,tokio1-rustls-tls,tokio1_boring,tokio1_crate,tokio1_rustls,tracing,uuid,webpki-roots
-  
+        run: cargo test --no-default-features --features async-std1,async-std1-rustls,aws-lc-rs,rustls-native-certs,boring-tls,builder,dkim,file-transport,file-transport-envelope,hostname,mime03,pool,rustls-native-certs,rustls,sendmail-transport,smtp-transport,tokio1,tokio1-boring-tls,tokio1-rustls,tracing
+
       - name: Test with all features (-boring-tls)
-        run: cargo test --no-default-features --features async-std,async-std1,async-std1-rustls-tls,async-trait,base64,builder,dkim,ed25519-dalek,email-encoding,fastrand,file-transport,file-transport-envelope,futures-io,futures-rustls,futures-util,hostname,httpdate,mime,mime03,native-tls,nom,once_cell,pool,quoted_printable,rsa,rustls,rustls-pemfile,rustls-tls,sendmail-transport,serde,serde_json,sha2,smtp-transport,socket2,tokio1,tokio1-native-tls,tokio1-rustls-tls,tokio1_crate,tokio1_native_tls_crate,tokio1_rustls,tracing,uuid,webpki-roots
+        run: cargo test --no-default-features --features async-std1,async-std1-rustls,aws-lc-rs,rustls-native-certs,builder,dkim,file-transport,file-transport-envelope,hostname,mime03,native-tls,pool,rustls-native-certs,rustls,sendmail-transport,smtp-transport,tokio1,tokio1-native-tls,tokio1-rustls,tracing
 
 #  coverage:
 #    name: Coverage
 #    runs-on: ubuntu-latest
 #    steps:
-#      - uses: actions/checkout@v2
+#      - uses: actions/checkout@v4
 #      - uses: actions-rs/toolchain@v1
 #        with:
 #          toolchain: nightly

.gitignore

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

CHANGELOG.md

@@ -1,3 +1,441 @@
+<a name="v0.11.17"></a>
+### v0.11.17 (2025-06-06)
+
+#### Features
+
+* Add support for `rustls-platform-verifier` ([#1081])
+
+#### Misc
+
+* Change readme example to use `Mailbox::new` instead of string parsing ([#1090])
+* Replace futures-util `Mutex` with std `Mutex` in `AsyncStubTransport` ([#1091])
+* Avoid duplicate `abort_concurrent` implementation ([#1092])
+
+[#1081]: https://github.com/lettre/lettre/pull/1081
+[#1090]: https://github.com/lettre/lettre/pull/1090
+[#1091]: https://github.com/lettre/lettre/pull/1091
+[#1092]: https://github.com/lettre/lettre/pull/1092
+
+<a name="v0.11.16"></a>
+### v0.11.16 (2025-05-12)
+
+#### Features
+
+* Always implement `Clone` for `AsyncFileTransport` ([#1075])
+
+#### Changes
+
+* `Tls`, `CertificateStore`, `TlsParameters`, `TlsParametersBuilder`, `Certificate` and `Identity`
+  are now marked as deprecated when no TLS backend is enabled. They will be properly feature gated
+  in lettre v0.12 ([#1084])
+
+#### Misc
+
+* Gate `web-time` behind `cfg(target_arch = "wasm32")]` ([#1086])
+* Add missing `#[doc(cfg(...))]` attributes ([#1086])
+* Upgrade `webpki-roots` to v1 ([#1088])
+* Cleanup internal `TlsParameters` and `(Async)NetworkStream` structures ([#1082])
+* Feature gate internal `TransportBuilder::tls` to avoid recursive call site warnings ([#1083])
+* Fix workaround for embedding cargo script in rustdoc output ([#1077])
+* Fix `clippy::io_other_error` warnings ([#1078])
+* Upgrade semver compatible dependencies ([#1076], [#1079], [#1080])
+
+[#1075]: https://github.com/lettre/lettre/pull/1075
+[#1076]: https://github.com/lettre/lettre/pull/1076
+[#1077]: https://github.com/lettre/lettre/pull/1077
+[#1078]: https://github.com/lettre/lettre/pull/1078
+[#1079]: https://github.com/lettre/lettre/pull/1079
+[#1080]: https://github.com/lettre/lettre/pull/1080
+[#1082]: https://github.com/lettre/lettre/pull/1082
+[#1083]: https://github.com/lettre/lettre/pull/1083
+[#1084]: https://github.com/lettre/lettre/pull/1084
+[#1086]: https://github.com/lettre/lettre/pull/1086
+[#1088]: https://github.com/lettre/lettre/pull/1088
+
+<a name="v0.11.15"></a>
+### v0.11.15 (2025-03-10)
+
+#### Upgrade notes
+
+* MSRV is now 1.74 ([#1060])
+
+#### Features
+
+* Add controlled shutdown methods ([#1045], [#1068])
+
+#### Misc
+
+* Deny `unreachable_pub` lint ([#1058])
+* Bump minimum supported `rustls` ([#1063])
+* Bump minimum supported `serde` ([#1064])
+* Upgrade semver compatible dependencies ([#1067])
+* Upgrade `email-encoding` to v0.4 ([#1069])
+
+[#1045]: https://github.com/lettre/lettre/pull/1045
+[#1058]: https://github.com/lettre/lettre/pull/1058
+[#1060]: https://github.com/lettre/lettre/pull/1060
+[#1063]: https://github.com/lettre/lettre/pull/1063
+[#1064]: https://github.com/lettre/lettre/pull/1064
+[#1067]: https://github.com/lettre/lettre/pull/1067
+[#1068]: https://github.com/lettre/lettre/pull/1068
+[#1069]: https://github.com/lettre/lettre/pull/1069
+
+<a name="v0.11.14"></a>
+### v0.11.14 (2025-02-23)
+
+This release deprecates the `rustls-tls`, `tokio1-rustls-tls` and `async-std1-rustls-tls`
+features, which will be removed in lettre v0.12.
+
+rustls users should start migrating to the `rustls`, `tokio1-rustls` and
+`async-std1-rustls` features. Unlike the deprecated _*rustls-tls_ features,
+which automatically enabled the `ring` and `webpki-roots` backends, the new
+features do not. To complete the migration, users must either enable the
+`aws-lc-rs` or the `ring` feature. Additionally, those who rely on `webpki-roots`
+for TLS certificate verification must now explicitly enable its feature.
+Users of `rustls-native-certs` do not need to enable `webpki-roots`.
+
+Find out more about the new features via the [lettre rustls docs].
+
+#### Features
+
+* Make it possible to use different `rustls` crypto providers and TLS verifiers ([#1054])
+
+#### Bug fixes
+
+* Use the same `rustls` crypto provider everywhere ([#1055])
+
+#### Misc
+
+* Deprecate `AsyncNetworkStream` being public ([#1059])
+* Upgrade `nom` to v8 ([#1048])
+* Drop `rustls-pemfile` in favor of `rustls-pki-types` APIs ([#1050])
+* Ban direct use of `std::time::SystemTime::now` via clippy ([#1043])
+* Drop direct dependency on `rustls-pki-types` ([#1051])
+* Remove artifact from `web-time` refactor ([#1049])
+* Fix warnings with `rustls-native-certs` when `tracing` is disabled ([#1053])
+* Bump license year ([#1057])
+* Cleanup `Cargo.toml` style ([#1047])
+
+[lettre rustls docs]: https://docs.rs/lettre/0.11.14/lettre/index.html#smtp-over-tls-via-the-rustls-crate
+[#1043]: https://github.com/lettre/lettre/pull/1043
+[#1047]: https://github.com/lettre/lettre/pull/1047
+[#1048]: https://github.com/lettre/lettre/pull/1048
+[#1049]: https://github.com/lettre/lettre/pull/1049
+[#1050]: https://github.com/lettre/lettre/pull/1050
+[#1051]: https://github.com/lettre/lettre/pull/1051
+[#1053]: https://github.com/lettre/lettre/pull/1053
+[#1054]: https://github.com/lettre/lettre/pull/1054
+[#1055]: https://github.com/lettre/lettre/pull/1055
+[#1057]: https://github.com/lettre/lettre/pull/1057
+[#1059]: https://github.com/lettre/lettre/pull/1059
+
+<a name="v0.11.13"></a>
+### v0.11.13 (2025-02-17)
+
+#### Features
+
+* Add WASM support ([#1037], [#1042])
+* Add method to get the TLS verify result with BoringSSL ([#1039])
+
+#### Bug fixes
+
+* Synchronous pool shutdowns being arbitrarily delayed ([#1041])
+
+[#1037]: https://github.com/lettre/lettre/pull/1037
+[#1039]: https://github.com/lettre/lettre/pull/1039
+[#1041]: https://github.com/lettre/lettre/pull/1041
+[#1042]: https://github.com/lettre/lettre/pull/1042
+
+<a name="v0.11.12"></a>
+### v0.11.12 (2025-02-02)
+
+#### Misc
+
+* Warn against manually configuring `port` and `tls` on SMTP transport builder ([#1014])
+* Document variants of `Tls` enum ([#1015])
+* Fix rustdoc warnings ([#1016])
+* Add `ContentType::TEXT_PLAIN` to `Message` builder examples ([#1017])
+* Document `SmtpTransport` and `AsyncSmtpTransport` ([#1018])
+* Fix typo in transport builder `credentials` method ([#1019])
+* Document required system dependencies for OpenSSL ([#1030])
+* Improve docs for the `transport::smtp` module ([#1031])
+* Improve docs for smtp transport builder `from_url` ([#1032])
+* Replace `assert!` with `?` on `send` examples ([#1033])
+* Warn on more pedantic clippy lints and fix them ([#1035], [#1036])
+
+[#1014]: https://github.com/lettre/lettre/pull/1014
+[#1015]: https://github.com/lettre/lettre/pull/1015
+[#1016]: https://github.com/lettre/lettre/pull/1016
+[#1017]: https://github.com/lettre/lettre/pull/1017
+[#1018]: https://github.com/lettre/lettre/pull/1018
+[#1019]: https://github.com/lettre/lettre/pull/1019
+[#1030]: https://github.com/lettre/lettre/pull/1030
+[#1031]: https://github.com/lettre/lettre/pull/1031
+[#1032]: https://github.com/lettre/lettre/pull/1032
+[#1033]: https://github.com/lettre/lettre/pull/1033
+[#1035]: https://github.com/lettre/lettre/pull/1035
+[#1036]: https://github.com/lettre/lettre/pull/1036
+
+<a name="v0.11.11"></a>
+### v0.11.11 (2024-12-05)
+
+#### Upgrade notes
+
+* MSRV is now 1.71 ([#1008])
+
+#### Bug fixes
+
+* Fix off-by-one error reaching the minimum number of configured pooled connections ([#1012])
+
+#### Misc
+
+* Fix clippy warnings ([#1009])
+* Fix `-Zminimal-versions` build ([#1007])
+
+[#1007]: https://github.com/lettre/lettre/pull/1007
+[#1008]: https://github.com/lettre/lettre/pull/1008
+[#1009]: https://github.com/lettre/lettre/pull/1009
+[#1012]: https://github.com/lettre/lettre/pull/1012
+
+<a name="v0.11.10"></a>
+### v0.11.10 (2024-10-23)
+
+#### Bug fixes
+
+* Ignore disconnect errors when `pool` feature of SMTP transport is disabled ([#999])
+* Use case insensitive comparisons for matching login challenge requests ([#1000])
+
+[#999]: https://github.com/lettre/lettre/pull/999
+[#1000]: https://github.com/lettre/lettre/pull/1000
+
+<a name="v0.11.9"></a>
+### v0.11.9 (2024-09-13)
+
+#### Bug fixes
+
+* Fix feature gate for `accept_invalid_hostnames` for rustls ([#988])
+* Fix parsing `Mailbox` with trailing spaces ([#986])
+
+#### Misc
+
+* Bump `rustls-native-certs` to v0.8 ([#992])
+* Make getting started example in readme complete ([#990])
+
+[#988]: https://github.com/lettre/lettre/pull/988
+[#986]: https://github.com/lettre/lettre/pull/986
+[#990]: https://github.com/lettre/lettre/pull/990
+[#992]: https://github.com/lettre/lettre/pull/992
+
+<a name="v0.11.8"></a>
+### v0.11.8 (2024-09-03)
+
+#### Features
+
+* Add mTLS support ([#974])
+* Implement `accept_invalid_hostnames` for rustls ([#977])
+* Provide certificate chain for peer certificates when using `rustls` or `boring-tls` ([#976])
+
+#### Changes
+
+* Make `HeaderName` comparisons via `PartialEq` case insensitive ([#980])
+
+#### Misc
+
+* Fix clippy warnings ([#979])
+* Replace manual impl of `#[non_exhaustive]` for `InvalidHeaderName` ([#981])
+
+[#974]: https://github.com/lettre/lettre/pull/974
+[#976]: https://github.com/lettre/lettre/pull/976
+[#977]: https://github.com/lettre/lettre/pull/977
+[#980]: https://github.com/lettre/lettre/pull/980
+[#981]: https://github.com/lettre/lettre/pull/981
+
+<a name="v0.11.7"></a>
+### v0.11.7 (2024-04-23)
+
+#### Misc
+
+* Bump `hostname` to v0.4 ([#956])
+* Fix `tracing` message consistency ([#960])
+* Bump minimum required `rustls` to v0.23.5 ([#958])
+* Dropped use of `ref` syntax in the entire project ([#959])
+
+[#956]: https://github.com/lettre/lettre/pull/956
+[#958]: https://github.com/lettre/lettre/pull/958
+[#959]: https://github.com/lettre/lettre/pull/959
+[#960]: https://github.com/lettre/lettre/pull/960
+
+<a name="v0.11.6"></a>
+### v0.11.6 (2024-03-28)
+
+#### Bug fixes
+
+* Upgraded `email-encoding` to v0.3 - fixing multiple encoding bugs in the process ([#952])
+
+#### Misc
+
+* Updated copyright year in license ([#954])
+
+[#952]: https://github.com/lettre/lettre/pull/952
+[#954]: https://github.com/lettre/lettre/pull/954
+
+<a name="v0.11.5"></a>
+### v0.11.5 (2024-03-25)
+
+#### Features
+
+* Support SMTP SASL draft login challenge ([#911])
+* Add conversion from SMTP response code to integer ([#941])
+
+#### Misc
+
+* Upgrade `rustls` to v0.23 ([#950])
+* Bump `base64` to v0.22 ([#945])
+* Fix typos in documentation ([#943], [#944])
+* Add `Cargo.lock` ([#942])
+
+[#911]: https://github.com/lettre/lettre/pull/911
+[#941]: https://github.com/lettre/lettre/pull/941
+[#942]: https://github.com/lettre/lettre/pull/942
+[#943]: https://github.com/lettre/lettre/pull/943
+[#944]: https://github.com/lettre/lettre/pull/944
+[#945]: https://github.com/lettre/lettre/pull/945
+[#950]: https://github.com/lettre/lettre/pull/950
+
+<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)
 
@@ -110,7 +548,7 @@ 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>
@@ -280,6 +718,6 @@ Several breaking changes were made between 0.9 and 0.10, but changes should be s
 
 *  multipart support
 *  add non-consuming methods for Email builders
-* `add_header` does not return the builder anymore, 
+* `add_header` does not return the builder anymore,
   for consistency with other methods. Use the `header`
   method instead

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 = "0.10.2"
+version = "0.11.17"
 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 = "1.60"
+rust-version = "1.74"
 
 [badges]
 is-it-maintained-issue-resolution = { repository = "lettre/lettre" }
@@ -19,34 +19,39 @@ is-it-maintained-open-issues = { repository = "lettre/lettre" }
 maintenance = { status = "actively-developed" }
 
 [dependencies]
-idna = "0.3"
-once_cell = { version = "1", optional = true }
-tracing = { version = "0.1.16", default-features = false, features = ["std"], optional = true } # feature
+email_address = { version = "0.2.1", default-features = false }
+nom = "8"
+idna = "1"
+
+## tracing support
+tracing = { version = "0.1.16", default-features = false, features = ["std"], optional = true }
 
 # builder
 httpdate = { version = "1", optional = true }
 mime = { version = "0.3.4", optional = true }
-fastrand = { version = "1.4", optional = true }
-quoted_printable = { version = "0.4.6", optional = true }
-base64 = { version = "0.21", optional = true }
-email-encoding = { version = "0.2", optional = true }
+fastrand = { version = "2.0", optional = true }
+quoted_printable = { version = "0.5", optional = true }
+base64 = { version = "0.22", optional = true }
+email-encoding = { version = "0.4", optional = true }
 
 # file transport
 uuid = { version = "1", features = ["v4"], optional = true }
-serde = { version = "1", optional = true, features = ["derive"] }
+serde = { version = "1.0.110", features = ["derive"], optional = true }
 serde_json = { version = "1", optional = true }
 
 # smtp-transport
-nom = { version = "7", optional = true }
-hostname = { version = "0.3", optional = true } # feature
-socket2 = { version = "0.4.4", optional = true }
+hostname = { version = "0.4", optional = true } # feature
+socket2 = { version = "0.6", 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 }
-boring = { version = "2.0.0", optional = true }
+native-tls = { version = "0.2.9", optional = true } # feature
+rustls = { version = "0.23.18", default-features = false, features = ["logging", "std", "tls12"], optional = true }
+rustls-platform-verifier = { version = "0.6.0", optional = true }
+rustls-native-certs = { version = "0.8", optional = true }
+webpki-roots = { version = "1.0.0", optional = true }
+boring = { version = "4", optional = true }
 
 # async
 futures-io = { version = "0.3.7", optional = true }
@@ -55,26 +60,26 @@ async-trait = { version = "0.1", optional = true }
 
 ## async-std
 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 = "0.26", default-features = false, features = ["logging", "tls12"], optional = true }
 
 ## tokio
 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_boring = { package = "tokio-boring", version = "2.1.4", optional = true }
+tokio1_rustls = { package = "tokio-rustls", version = "0.26", default-features = false, features = ["logging", "tls12"], optional = true }
+tokio1_boring = { package = "tokio-boring", version = "4", optional = true }
 
 ## dkim
-sha2 = { version = "0.10", optional = true, features = ["oid"] }
-rsa = { version = "0.8", optional = true }
-ed25519-dalek = { version = "1.0.1", optional = true }
+sha2 = { version = "0.10", features = ["oid"], optional = true }
+rsa = { version = "0.9", optional = true }
+ed25519-dalek = { version = "2", optional = true }
 
-# email formats
-email_address = { version = "0.2.1", default-features = false }
+[target.'cfg(target_arch = "wasm32")'.dependencies]
+## web-time for wasm support
+web-time = { version = "1.1.0", optional = true }
 
 [dev-dependencies]
 pretty_assertions = "1"
-criterion = "0.4"
+criterion = "0.5"
 tracing = { version = "0.1.16", default-features = false, features = ["std"] }
 tracing-subscriber = "0.3"
 glob = "0.3"
@@ -82,39 +87,58 @@ walkdir = "2"
 tokio1_crate = { package = "tokio", version = "1", features = ["macros", "rt-multi-thread"] }
 async-std = { version = "1.8", features = ["attributes"] }
 serde_json = "1"
-maud = "0.24"
+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", "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", "tokio1_crate?/fs", "tokio1_crate?/io-util"]
-file-transport-envelope = ["serde", "serde_json", "file-transport"]
+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 = ["base64", "nom", "socket2", "once_cell", "tokio1_crate?/rt", "tokio1_crate?/time", "tokio1_crate?/net"]
+smtp-transport = ["dep:base64", "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 = ["dep:rustls"]
+aws-lc-rs = ["rustls?/aws-lc-rs"]
+fips = ["aws-lc-rs", "rustls?/fips"]
+ring = ["rustls?/ring"]
+webpki-roots = ["dep:webpki-roots"]
+# deprecated
+rustls-tls = ["webpki-roots", "rustls", "ring"]
 
-boring-tls = ["boring"]
+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"]
-tokio1-boring-tls = ["tokio1", "boring-tls", "tokio1_boring"]
+async-std1 = ["dep:async-std", "dep:async-trait", "dep:futures-io", "dep:futures-util"]
+async-std1-rustls = ["async-std1", "rustls", "dep:futures-rustls"]
+# deprecated
+async-std1-rustls-tls = ["async-std1-rustls", "rustls-tls"]
+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 = ["tokio1", "rustls", "dep:tokio1_rustls"]
+# deprecated
+tokio1-rustls-tls = ["tokio1-rustls", "rustls-tls"]
+tokio1-boring-tls = ["tokio1", "boring-tls", "dep:tokio1_boring"]
 
-dkim = ["base64", "sha2", "rsa", "ed25519-dalek"]
+dkim = ["dep:base64", "dep:sha2", "dep:rsa", "dep:ed25519-dalek"]
+
+# wasm support
+web = ["dep:web-time"]
+
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(lettre_ignore_tls_mismatch)'] }
 
 [package.metadata.docs.rs]
 all-features = true

LICENSE

@@ -1,5 +1,5 @@
-Copyright (c) 2014-2022 Alexis Mousset <contact@amousset.me>
-Copyright (c) 2019-2022 Paolo Barbolini <paolo@paolo565.org>
+Copyright (c) 2014-2024 Alexis Mousset <contact@amousset.me>
+Copyright (c) 2019-2025 Paolo Barbolini <paolo@paolo565.org>
 Copyright (c) 2018 K. <kayo@illumium.org>
 
 Permission is hereby granted, free of charge, to any

README.md

@@ -28,8 +28,8 @@
 </div>
 
 <div align="center">
-  <a href="https://deps.rs/crate/lettre/0.10.2">
-    <img src="https://deps.rs/crate/lettre/0.10.2/status.svg"
+  <a href="https://deps.rs/crate/lettre/0.11.17">
+    <img src="https://deps.rs/crate/lettre/0.11.17/status.svg"
       alt="dependency status" />
   </a>
 </div>
@@ -53,43 +53,47 @@ Lettre does not provide (for now):
 ## 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 1.60, but this could change at any time either from
+the minimum supported Rust version is 1.74, 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 1.60 or newer.
+This library requires Rust 1.74 or newer.
 To use this library, add the following to your `Cargo.toml`:
 
 ```toml
 [dependencies]
-lettre = "0.10"
+lettre = "0.11"
 ```
 
 ```rust,no_run
+use lettre::message::header::ContentType;
 use lettre::transport::smtp::authentication::Credentials;
 use lettre::{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")
-    .body(String::from("Be happy!"))
-    .unwrap();
+fn main() {
+    let email = Message::builder()
+        .from(Mailbox::new("NoBody".to_owned(), "nobody@domain.tld".parse().unwrap()))
+        .reply_to(Mailbox::new("Yuin".to_owned(), "yuin@domain.tld".parse().unwrap()))
+        .to(Mailbox::new("Hei".to_owned(), "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")
-    .unwrap()
-    .credentials(creds)
-    .build();
+    // Open a remote connection to gmail
+    let mailer = SmtpTransport::relay("smtp.gmail.com")
+        .unwrap()
+        .credentials(creds)
+        .build();
 
-// Send the email
-match mailer.send(&email) {
-    Ok(_) => println!("Email sent successfully!"),
-    Err(e) => panic!("Could not send email: {:?}", e),
+    // Send the email
+    match mailer.send(&email) {
+        Ok(_) => println!("Email sent successfully!"),
+        Err(e) => panic!("Could not send email: {e:?}"),
+    }
 }
 ```
 
@@ -103,7 +107,7 @@ 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 
+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 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);

benches/transport_smtp.rs

@@ -1,5 +1,5 @@
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
-use lettre::{Message, SmtpTransport, Transport};
+use lettre::{message::header::ContentType, Message, SmtpTransport, Transport};
 
 fn bench_simple_send(c: &mut Criterion) {
     let sender = SmtpTransport::builder_dangerous("127.0.0.1")
@@ -13,6 +13,7 @@ fn bench_simple_send(c: &mut Criterion) {
                 .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 result = black_box(sender.send(&email));
@@ -32,6 +33,7 @@ fn bench_reuse_send(c: &mut Criterion) {
                 .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 result = black_box(sender.send(&email));

clippy.toml

@@ -0,0 +1,3 @@
+disallowed-methods = [
+    { "path" = "std::time::SystemTime::now", reason = "does not work on WASM environments", replacement = "crate::time::now" }
+]

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> =

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> =

examples/autoconfigure.rs

@@ -41,7 +41,7 @@ fn main() {
 
     // 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);
+        tracing::info!("Trying to establish a plaintext connection to {} and then upgrading it via the SMTP STARTTLS extension", smtp_host);
 
         let transport = SmtpTransport::starttls_relay(&smtp_host)
             .expect("build SmtpTransport::starttls_relay")

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();
 

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")

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")

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")

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> =

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> =

src/address/envelope.rs

@@ -14,11 +14,71 @@ pub struct Envelope {
     /// The envelope recipient's addresses
     ///
     /// This can not be empty.
+    #[cfg_attr(
+        feature = "serde",
+        serde(deserialize_with = "serde_forward_path::deserialize")
+    )]
     forward_path: Vec<Address>,
     /// The envelope sender address
     reverse_path: Option<Address>,
 }
 
+/// just like the default implementation to deserialize `Vec<Address>` but it
+/// forbids **de**serializing empty lists
+#[cfg(feature = "serde")]
+mod serde_forward_path {
+    use super::Address;
+    /// dummy type required for serde
+    /// see example: <https://serde.rs/deserialize-map.html>
+    struct CustomVisitor;
+    impl<'de> serde::de::Visitor<'de> for CustomVisitor {
+        type Value = Vec<Address>;
+
+        fn expecting(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            formatter.write_str("a non-empty list of recipient addresses")
+        }
+
+        fn visit_seq<S>(self, mut access: S) -> Result<Self::Value, S::Error>
+        where
+            S: serde::de::SeqAccess<'de>,
+        {
+            let mut seq: Vec<Address> = Vec::with_capacity(access.size_hint().unwrap_or(0));
+            while let Some(key) = access.next_element()? {
+                seq.push(key);
+            }
+            if seq.is_empty() {
+                Err(serde::de::Error::invalid_length(seq.len(), &self))
+            } else {
+                Ok(seq)
+            }
+        }
+    }
+    pub(super) fn deserialize<'de, D>(deserializer: D) -> Result<Vec<Address>, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        deserializer.deserialize_seq(CustomVisitor {})
+    }
+
+    #[cfg(test)]
+    mod tests {
+        #[test]
+        fn deserializing_empty_recipient_list_returns_error() {
+            assert!(
+                serde_json::from_str::<crate::address::Envelope>(r#"{"forward_path": []}"#)
+                    .is_err()
+            );
+        }
+        #[test]
+        fn deserializing_non_empty_recipient_list_is_ok() {
+            serde_json::from_str::<crate::address::Envelope>(
+                r#"{ "forward_path": [ {"user":"foo", "domain":"example.com"} ] }"#,
+            )
+            .unwrap();
+        }
+    }
+}
+
 impl Envelope {
     /// Creates a new envelope, which may fail if `to` is empty.
     ///
@@ -103,6 +163,7 @@ impl Envelope {
 }
 
 #[cfg(feature = "builder")]
+#[cfg_attr(docsrs, doc(cfg(feature = "builder")))]
 impl TryFrom<&Headers> for Envelope {
     type Error = Error;
 

src/address/serde.rs

@@ -36,7 +36,7 @@ impl<'de> Deserialize<'de> for Address {
             {
                 struct FieldVisitor;
 
-                impl<'de> Visitor<'de> for FieldVisitor {
+                impl Visitor<'_> for FieldVisitor {
                     type Value = Field;
 
                     fn expecting(&self, formatter: &mut Formatter<'_>) -> FmtResult {

src/address/types.rs

@@ -15,7 +15,7 @@ use idna::domain_to_ascii;
 ///
 /// 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
 ///
@@ -227,6 +227,7 @@ fn check_address(val: &str) -> Result<usize, AddressError> {
 }
 
 #[derive(Debug, PartialEq, Eq, Clone, Copy)]
+#[non_exhaustive]
 /// Errors in email addresses parsing
 pub enum AddressError {
     /// Missing domain or user
@@ -237,6 +238,8 @@ pub enum AddressError {
     InvalidUser,
     /// Invalid email domain
     InvalidDomain,
+    /// Invalid input found
+    InvalidInput,
 }
 
 impl Error for AddressError {}
@@ -248,6 +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"),
         }
     }
 }

src/executor.rs

@@ -45,6 +45,7 @@ use crate::transport::smtp::Error;
 #[async_trait]
 pub trait Executor: Debug + Send + Sync + 'static + private::Sealed {
     #[cfg(feature = "smtp-transport")]
+    #[allow(private_bounds)]
     type Handle: SpawnHandle;
     #[cfg(feature = "smtp-transport")]
     type Sleep: Future<Output = ()> + Send + 'static;
@@ -82,8 +83,8 @@ pub trait Executor: Debug + Send + Sync + 'static + private::Sealed {
 #[doc(hidden)]
 #[cfg(feature = "smtp-transport")]
 #[async_trait]
-pub trait SpawnHandle: Debug + Send + Sync + 'static + private::Sealed {
-    async fn shutdown(self);
+pub(crate) trait SpawnHandle: Debug + Send + Sync + 'static + private::Sealed {
+    async fn shutdown(&self);
 }
 
 /// Async [`Executor`] using `tokio` `1.x`
@@ -133,8 +134,8 @@ impl Executor for Tokio1Executor {
     ) -> Result<AsyncSmtpConnection, Error> {
         #[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()),
+            #[cfg(any(feature = "tokio1-native-tls", feature = "tokio1-rustls"))]
+            Tls::Wrapper(tls_parameters) => Some(tls_parameters.clone()),
             _ => None,
         };
         #[allow(unused_mut)]
@@ -147,14 +148,14 @@ impl Executor for Tokio1Executor {
         )
         .await?;
 
-        #[cfg(any(feature = "tokio1-native-tls", feature = "tokio1-rustls-tls"))]
+        #[cfg(any(feature = "tokio1-native-tls", feature = "tokio1-rustls"))]
         match tls {
-            Tls::Opportunistic(ref tls_parameters) => {
+            Tls::Opportunistic(tls_parameters) => {
                 if conn.can_starttls() {
                     conn.starttls(tls_parameters.clone(), hello_name).await?;
                 }
             }
-            Tls::Required(ref tls_parameters) => {
+            Tls::Required(tls_parameters) => {
                 conn.starttls(tls_parameters.clone(), hello_name).await?;
             }
             _ => (),
@@ -177,7 +178,7 @@ impl Executor for Tokio1Executor {
 #[cfg(all(feature = "smtp-transport", feature = "tokio1"))]
 #[async_trait]
 impl SpawnHandle for tokio1_crate::task::JoinHandle<()> {
-    async fn shutdown(self) {
+    async fn shutdown(&self) {
         self.abort();
     }
 }
@@ -201,7 +202,7 @@ pub struct AsyncStd1Executor;
 #[cfg(feature = "async-std1")]
 impl Executor for AsyncStd1Executor {
     #[cfg(feature = "smtp-transport")]
-    type Handle = async_std::task::JoinHandle<()>;
+    type Handle = futures_util::future::AbortHandle;
     #[cfg(feature = "smtp-transport")]
     type Sleep = BoxFuture<'static, ()>;
 
@@ -211,12 +212,14 @@ impl Executor for AsyncStd1Executor {
         F: Future<Output = ()> + Send + 'static,
         F::Output: Send + 'static,
     {
-        async_std::task::spawn(fut)
+        let (handle, registration) = futures_util::future::AbortHandle::new_pair();
+        async_std::task::spawn(futures_util::future::Abortable::new(fut, registration));
+        handle
     }
 
     #[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)
     }
 
@@ -230,8 +233,8 @@ impl Executor for AsyncStd1Executor {
     ) -> Result<AsyncSmtpConnection, Error> {
         #[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()),
+            #[cfg(feature = "async-std1-rustls")]
+            Tls::Wrapper(tls_parameters) => Some(tls_parameters.clone()),
             _ => None,
         };
         #[allow(unused_mut)]
@@ -243,14 +246,14 @@ impl Executor for AsyncStd1Executor {
         )
         .await?;
 
-        #[cfg(any(feature = "async-std1-native-tls", feature = "async-std1-rustls-tls"))]
+        #[cfg(feature = "async-std1-rustls")]
         match tls {
-            Tls::Opportunistic(ref tls_parameters) => {
+            Tls::Opportunistic(tls_parameters) => {
                 if conn.can_starttls() {
                     conn.starttls(tls_parameters.clone(), hello_name).await?;
                 }
             }
-            Tls::Required(ref tls_parameters) => {
+            Tls::Required(tls_parameters) => {
                 conn.starttls(tls_parameters.clone(), hello_name).await?;
             }
             _ => (),
@@ -272,9 +275,9 @@ impl Executor for AsyncStd1Executor {
 
 #[cfg(all(feature = "smtp-transport", feature = "async-std1"))]
 #[async_trait]
-impl SpawnHandle for async_std::task::JoinHandle<()> {
-    async fn shutdown(self) {
-        self.cancel().await;
+impl SpawnHandle for futures_util::future::AbortHandle {
+    async fn shutdown(&self) {
+        self.abort();
     }
 }
 
@@ -291,5 +294,5 @@ mod private {
     impl Sealed for tokio1_crate::task::JoinHandle<()> {}
 
     #[cfg(all(feature = "smtp-transport", feature = "async-std1"))]
-    impl Sealed for async_std::task::JoinHandle<()> {}
+    impl Sealed for futures_util::future::AbortHandle {}
 }

src/lib.rs

@@ -6,7 +6,7 @@
 //! * Secure defaults
 //! * Async support
 //!
-//! Lettre requires Rust 1.60 or newer.
+//! Lettre requires Rust 1.74 or newer.
 //!
 //! ## Features
 //!
@@ -34,13 +34,25 @@
 //!
 //! _Secure SMTP connections using TLS from the `native-tls` crate_
 //!
-//! Uses schannel on Windows, Security-Framework on macOS, and OpenSSL on Linux.
+//! Uses schannel on Windows, Security-Framework on macOS, and OpenSSL
+//! on all other platforms.
 //!
 //! * **native-tls** 📫: TLS support for the synchronous version of the API
 //! * **tokio1-native-tls**: TLS support for the `tokio1` async version of the API
 //!
 //! NOTE: native-tls isn't supported with `async-std`
 //!
+//! ##### Building lettre with OpenSSL
+//!
+//! When building lettre with native-tls on a system that makes
+//! use of OpenSSL, the following packages will need to be installed
+//! in order for the build and the compiled program to run properly.
+//!
+//! | Distro       | Build-time packages        | Runtime packages             |
+//! | ------------ | -------------------------- | ---------------------------- |
+//! | Debian       | `pkg-config`, `libssl-dev` | `libssl3`, `ca-certificates` |
+//! | Alpine Linux | `pkgconf`, `openssl-dev`   | `libssl3`, `ca-certificates` |
+//!
 //! #### SMTP over TLS via the boring crate (Boring TLS)
 //!
 //! _Secure SMTP connections using TLS from the `boring-tls` crate_
@@ -52,13 +64,49 @@
 //!
 //! #### SMTP over TLS via the rustls crate
 //!
-//! _Secure SMTP connections using TLS from the `rustls-tls` crate_
+//! _Secure SMTP connections using TLS from the `rustls` crate_
 //!
-//! Rustls uses [ring] as the cryptography implementation. As a result, [not all Rust's targets are supported][ring-support].
+//! * **rustls**: TLS support for the synchronous version of the API
+//! * **tokio1-rustls**: TLS support for the `tokio1` async version of the API
+//! * **async-std1-rustls**: TLS support for the `async-std1` async version of the API
 //!
-//! * **rustls-tls**: TLS support for the synchronous version of the API
-//! * **tokio1-rustls-tls**: TLS support for the `tokio1` async version of the API
-//! * **async-std1-rustls-tls**: TLS support for the `async-std1` async version of the API
+//! ##### rustls crypto backends
+//!
+//! _The crypto implementation to use with rustls_
+//!
+//! When the `rustls` feature is enabled, one of the following crypto backends MUST also
+//! be enabled.
+//!
+//! * **aws-lc-rs**: use [AWS-LC] (via [`aws-lc-rs`]) as the `rustls` crypto backend
+//! * **ring**: use [`ring`] as the `rustls` crypto backend
+//!
+//! When enabling `aws-lc-rs`, the `fips` feature can also be enabled to have
+//! rustls use the FIPS certified module of AWS-LC.
+//!
+//! `aws-lc-rs` may require cmake on some platforms to compile.
+//! `fips` always requires cmake and the Go compiler to compile.
+//!
+//! ##### rustls certificate verification backend
+//!
+//! _The TLS certificate verification backend to use with rustls_
+//!
+//! When the `rustls` feature is enabled, one of the following verification backends
+//! MUST also be enabled.
+//!
+//! * **rustls-platform-verifier**: verify TLS certificate using the OS's native certificate store (see [`rustls-platform-verifier`])
+//! * **rustls-native-certs**: verify TLS certificates using the platform's native certificate store (see [`rustls-native-certs`]) - when in doubt use `rustls-platform-verifier`
+//! * **webpki-roots**: verify TLS certificates against Mozilla's root certificates (see [`webpki-roots`])
+//!
+//! The following packages will need to be installed in order for the build
+//! stage and the compiled program to run properly.
+//!
+//! | Verification backend       | Distro       | Build-time packages        | Runtime packages             |
+//! | ---------------------      | ------------ | -------------------------- | ---------------------------- |
+//! | `rustls-platform-verifier` | Debian       | none                       | `ca-certificates`            |
+//! | `rustls-platform-verifier` | Alpine Linux | none                       | `ca-certificates`            |
+//! | `rustls-native-certs`      | Debian       | none                       | `ca-certificates`            |
+//! | `rustls-native-certs`      | Alpine Linux | none                       | `ca-certificates`            |
+//! | `webpki-roots`             | any          | none                       | none                         |
 //!
 //! ### Sendmail transport
 //!
@@ -95,6 +143,7 @@
 //! * **tracing**: Logging using the `tracing` crate
 //! * **mime03**: Allow creating a [`ContentType`] from an existing [mime 0.3] `Mime` struct
 //! * **dkim**: Add support for signing email with DKIM
+//! * **web**: WebAssembly support using the `web-time` crate for time operations
 //!
 //! [`SMTP`]: crate::transport::smtp
 //! [`sendmail`]: crate::transport::sendmail
@@ -102,18 +151,23 @@
 //! [`ContentType`]: crate::message::header::ContentType
 //! [tokio]: https://docs.rs/tokio/1
 //! [async-std]: https://docs.rs/async-std/1
-//! [ring]: https://github.com/briansmith/ring#ring
-//! [ring-support]: https://github.com/briansmith/ring#online-automated-testing
+//! [AWS-LC]: https://github.com/aws/aws-lc
+//! [`aws-lc-rs`]: https://crates.io/crates/aws-lc-rs
+//! [`ring`]: https://crates.io/crates/ring
+//! [`rustls-platform-verifier`]: https://crates.io/crates/rustls-platform-verifier
+//! [`rustls-native-certs`]: https://crates.io/crates/rustls-native-certs
+//! [`webpki-roots`]: https://crates.io/crates/webpki-roots
 //! [Tokio 1.x]: https://docs.rs/tokio/1
 //! [async-std 1.x]: https://docs.rs/async-std/1
 //! [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/0.10.2")]
+#![doc(html_root_url = "https://docs.rs/crate/lettre/0.11.17")]
 #![doc(html_favicon_url = "https://lettre.rs/favicon.ico")]
 #![doc(html_logo_url = "https://avatars0.githubusercontent.com/u/15113230?v=4")]
 #![forbid(unsafe_code)]
 #![deny(
+    unreachable_pub,
     missing_copy_implementations,
     trivial_casts,
     trivial_numeric_casts,
@@ -135,12 +189,38 @@
     clippy::manual_assert,
     clippy::unnecessary_join,
     clippy::wildcard_imports,
-    clippy::zero_sized_map_values
+    clippy::str_to_string,
+    clippy::empty_structs_with_brackets,
+    clippy::zero_sized_map_values,
+    clippy::manual_let_else,
+    clippy::semicolon_if_nothing_returned,
+    clippy::unnecessary_wraps,
+    clippy::doc_markdown,
+    clippy::explicit_iter_loop,
+    clippy::redundant_closure_for_method_calls,
+    // Rust 1.86: clippy::unnecessary_semicolon,
 )]
 #![cfg_attr(docsrs, feature(doc_cfg))]
 
 #[cfg(not(lettre_ignore_tls_mismatch))]
 mod compiletime_checks {
+    #[cfg(all(feature = "rustls", not(feature = "aws-lc-rs"), not(feature = "ring")))]
+    compile_error!(
+        "feature `rustls` also requires either the `aws-lc-rs` or the `ring` feature to
+    be enabled"
+    );
+
+    #[cfg(all(
+        feature = "rustls",
+        not(feature = "rustls-platform-verifier"),
+        not(feature = "rustls-native-certs"),
+        not(feature = "webpki-roots")
+    ))]
+    compile_error!(
+        "feature `rustls` also requires either the `rustls-platform-verifier`, the `rustls-native-certs`
+    or the `webpki-roots` feature to be enabled"
+    );
+
     #[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.");
@@ -151,16 +231,12 @@ mod compiletime_checks {
         not(feature = "tokio1-native-tls")
     ))]
     compile_error!("Lettre is being built with the `tokio1` and the `native-tls` features, but the `tokio1-native-tls` feature hasn't been turned on.
-    If you were trying to opt into `rustls-tls` and did not activate `native-tls`, disable the default-features of lettre in `Cargo.toml` and manually add the required features.
+    If you were trying to opt into `rustls` and did not activate `native-tls`, disable the default-features of lettre in `Cargo.toml` and manually add the required features.
     Make sure to apply the same to any of your crate dependencies that use the `lettre` crate.");
 
-    #[cfg(all(
-        feature = "tokio1",
-        feature = "rustls-tls",
-        not(feature = "tokio1-rustls-tls")
-    ))]
-    compile_error!("Lettre is being built with the `tokio1` and the `rustls-tls` features, but the `tokio1-rustls-tls` feature hasn't been turned on.
-    If you'd like to use `native-tls` make sure that the `rustls-tls` feature hasn't been enabled by mistake.
+    #[cfg(all(feature = "tokio1", feature = "rustls", not(feature = "tokio1-rustls")))]
+    compile_error!("Lettre is being built with the `tokio1` and the `rustls` features, but the `tokio1-rustls` feature hasn't been turned on.
+    If you'd like to use `native-tls` make sure that the `rustls` 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(
@@ -169,36 +245,22 @@ mod compiletime_checks {
         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.
+    If you'd like to use `boring-tls` make sure that the `rustls` 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",
-        feature = "native-tls",
-        not(feature = "async-std1-native-tls")
-    ))]
-    compile_error!("Lettre is being built with the `async-std1` and the `native-tls` features, but the `async-std1-native-tls` feature hasn't been turned on.
-    If you'd like to use rustls make sure that the `native-tls` hasn't been enabled by mistake (you may need to import lettre without default features)
-    If you're building a library which depends on lettre import it without default features and enable just the features you need.");
-    */
-    #[cfg(all(
-        feature = "async-std1",
-        feature = "native-tls",
-        not(feature = "async-std1-native-tls")
-    ))]
+    #[cfg(all(feature = "async-std1", feature = "native-tls"))]
     compile_error!("Lettre is being built with the `async-std1` and the `native-tls` features, but the async-std integration doesn't support native-tls yet.
 If you'd like to work on the issue please take a look at https://github.com/lettre/lettre/issues/576.
-If you were trying to opt into `rustls-tls` and did not activate `native-tls`, disable the default-features of lettre in `Cargo.toml` and manually add the required features.
+If you were trying to opt into `rustls` and did not activate `native-tls`, disable the default-features of lettre in `Cargo.toml` and manually add the required features.
 Make sure to apply the same to any of your crate dependencies that use the `lettre` crate.");
 
     #[cfg(all(
         feature = "async-std1",
-        feature = "rustls-tls",
-        not(feature = "async-std1-rustls-tls")
+        feature = "rustls",
+        not(feature = "async-std1-rustls")
     ))]
-    compile_error!("Lettre is being built with the `async-std1` and the `rustls-tls` features, but the `async-std1-rustls-tls` feature hasn't been turned on.
-If you'd like to use `native-tls` make sure that the `rustls-tls` hasn't been enabled by mistake.
+    compile_error!("Lettre is being built with the `async-std1` and the `rustls` features, but the `async-std1-rustls` feature hasn't been turned on.
+If you'd like to use `native-tls` make sure that the `rustls` hasn't been enabled by mistake.
 Make sure to apply the same to any of your crate dependencies that use the `lettre` crate.");
 }
 
@@ -211,17 +273,20 @@ mod executor;
 #[cfg(feature = "builder")]
 #[cfg_attr(docsrs, doc(cfg(feature = "builder")))]
 pub mod message;
+#[cfg(feature = "rustls")]
+mod rustls_crypto;
+mod time;
 pub mod transport;
 
 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),
 }
 

src/message/body.rs

@@ -496,7 +496,7 @@ mod test {
     #[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

@@ -2,7 +2,6 @@ use std::{
     borrow::Cow,
     error::Error as StdError,
     fmt::{self, Display},
-    iter::IntoIterator,
     time::SystemTime,
 };
 
@@ -70,7 +69,7 @@ impl Display for DkimSigningAlgorithm {
     }
 }
 
-/// Describe DkimSigning key error
+/// Describe [`DkimSigningKey`] key error
 #[derive(Debug)]
 pub struct DkimSigningKeyError(InnerDkimSigningKeyError);
 
@@ -101,14 +100,14 @@ impl StdError for DkimSigningKeyError {
     }
 }
 
-/// Describe a signing key to be carried by DkimConfig struct
+/// Describe a signing key to be carried by [`DkimConfig`] struct
 #[derive(Debug)]
 pub struct DkimSigningKey(InnerDkimSigningKey);
 
 #[derive(Debug)]
 enum InnerDkimSigningKey {
     Rsa(RsaPrivateKey),
-    Ed25519(ed25519_dalek::Keypair),
+    Ed25519(ed25519_dalek::SigningKey),
 }
 
 impl DkimSigningKey {
@@ -121,14 +120,18 @@ impl DkimSigningKey {
                 RsaPrivateKey::from_pkcs1_pem(private_key)
                     .map_err(|err| DkimSigningKeyError(InnerDkimSigningKeyError::Rsa(err)))?,
             ),
-            DkimSigningAlgorithm::Ed25519 => InnerDkimSigningKey::Ed25519(
-                ed25519_dalek::Keypair::from_bytes(
-                    &crate::base64::decode(private_key).map_err(|err| {
-                        DkimSigningKeyError(InnerDkimSigningKeyError::Base64(err))
-                    })?,
-                )
-                .map_err(|err| DkimSigningKeyError(InnerDkimSigningKeyError::Ed25519(err)))?,
-            ),
+            DkimSigningAlgorithm::Ed25519 => {
+                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(),
+                            ))
+                        })?,
+                ))
+            }
         }))
     }
     fn get_signing_algorithm(&self) -> DkimSigningAlgorithm {
@@ -140,19 +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,
 }
 
@@ -181,7 +183,7 @@ impl DkimConfig {
         }
     }
 
-    /// Create a DkimConfig
+    /// Create a [`DkimConfig`]
     pub fn new(
         selector: String,
         domain: String,
@@ -281,19 +283,19 @@ fn dkim_canonicalize_headers_relaxed(headers: &str) -> String {
             // End of header.
             [b'\r', b'\n', ..] => {
                 *out += "\r\n";
-                name(&h[2..], out)
+                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)
+                value(&h[1..], out);
             }
             [_, ..] => {
                 let mut chars = h.chars();
                 out.push(chars.next().unwrap());
-                value(chars.as_str(), out)
+                value(chars.as_str(), out);
             }
             [] => {}
         }
@@ -315,7 +317,7 @@ fn dkim_canonicalize_header_tag(
     }
 }
 
-/// Canonicalize signed headers passed as headers_list among mail_headers using canonicalization
+/// Canonicalize signed headers passed as `headers_list` among `mail_headers` using canonicalization
 fn dkim_canonicalize_headers<'a>(
     headers_list: impl IntoIterator<Item = &'a str>,
     mail_headers: &Headers,
@@ -341,11 +343,10 @@ fn dkim_canonicalize_headers<'a>(
     }
 }
 
-/// Sign with Dkim a message by adding Dkim-Signture header created with configuration expressed by
-/// dkim_config
-
+/// Sign with Dkim a message by adding Dkim-Signature header created with configuration expressed by
+/// `dkim_config`
 pub fn dkim_sign(message: &mut Message, dkim_config: &DkimConfig) {
-    dkim_sign_fixed_time(message, dkim_config, SystemTime::now())
+    dkim_sign_fixed_time(message, dkim_config, crate::time::now());
 }
 
 fn dkim_sign_fixed_time(message: &mut Message, dkim_config: &DkimConfig, timestamp: SystemTime) {
@@ -376,7 +377,7 @@ fn dkim_sign_fixed_time(message: &mut Message, dkim_config: &DkimConfig, timesta
     }
     let dkim_header = dkim_header_format(dkim_config, timestamp, &signed_headers_list, &bh, "");
     let signed_headers = dkim_canonicalize_headers(
-        dkim_config.headers.iter().map(|h| h.as_ref()),
+        dkim_config.headers.iter().map(AsRef::as_ref),
         headers,
         dkim_config.canonicalization.header,
     );
@@ -477,23 +478,23 @@ cJ5Ku0OTwRtSMaseRPX+T4EfG1Caa/eunPPN4rh+CSup2BVVarOT
             .from("Test O'Leary <test+ezrz@example.net>".parse().unwrap())
             .to("Test2 <test2@example.org>".parse().unwrap())
             .date(std::time::UNIX_EPOCH)
-            .header(TestHeader("test  test very very long with spaces and extra spaces   \twill be folded to several lines ".to_string()))
+            .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();
         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")
+        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();
         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")
+        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]
@@ -521,8 +522,8 @@ cJ5Ku0OTwRtSMaseRPX+T4EfG1Caa/eunPPN4rh+CSup2BVVarOT
         dkim_sign_fixed_time(
             &mut message,
             &DkimConfig::new(
-                "dkimtest".to_string(),
-                "example.org".to_string(),
+                "dkimtest".to_owned(),
+                "example.org".to_owned(),
                 signing_key,
                 vec![
                     HeaderName::new_from_ascii_str("Date"),
@@ -570,8 +571,8 @@ cJ5Ku0OTwRtSMaseRPX+T4EfG1Caa/eunPPN4rh+CSup2BVVarOT
         dkim_sign_fixed_time(
             &mut message,
             &DkimConfig::new(
-                "dkimtest".to_string(),
-                "example.org".to_string(),
+                "dkimtest".to_owned(),
+                "example.org".to_owned(),
                 signing_key,
                 vec![
                     HeaderName::new_from_ascii_str("Date"),

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,
@@ -67,12 +69,6 @@ impl FromStr for ContentTransferEncoding {
     }
 }
 
-impl Default for ContentTransferEncoding {
-    fn default() -> Self {
-        ContentTransferEncoding::Base64
-    }
-}
-
 #[cfg(test)]
 mod test {
     use pretty_assertions::assert_eq;
@@ -99,7 +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!(
@@ -109,7 +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

@@ -1,6 +1,6 @@
 use std::fmt::Write;
 
-use email_encoding::headers::EmailWriter;
+use email_encoding::headers::writer::EmailWriter;
 
 use super::{Header, HeaderName, HeaderValue};
 use crate::BoxError;
@@ -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)
     }
@@ -38,10 +38,10 @@ impl ContentDisposition {
         let mut encoded_value = String::new();
         let line_len = "Content-Disposition: ".len();
         {
-            let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false, false);
+            let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false);
             w.write_str(kind).expect("writing `kind` returned an error");
             w.write_char(';').expect("writing `;` returned an error");
-            w.optional_breakpoint();
+            w.space();
 
             email_encoding::headers::rfc2231::encode("filename", file_name, &mut w)
                 .expect("some Write implementation returned an error");
@@ -106,7 +106,7 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Disposition"),
-            "inline".to_string(),
+            "inline".to_owned(),
         ));
 
         assert_eq!(
@@ -116,7 +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);
 
@@ -119,7 +119,7 @@ mod serde {
         {
             struct ContentTypeVisitor;
 
-            impl<'de> Visitor<'de> for ContentTypeVisitor {
+            impl Visitor<'_> for ContentTypeVisitor {
                 type Value = ContentType;
 
                 // The error message which states what the Visitor expects to
@@ -178,14 +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

@@ -21,7 +21,7 @@ impl Date {
     ///
     /// Shortcut for `Date::new(SystemTime::now())`
     pub fn now() -> Self {
-        Self::new(SystemTime::now())
+        Self::new(crate::time::now())
     }
 }
 
@@ -90,7 +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
@@ -110,7 +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!(
@@ -122,7 +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

@@ -1,4 +1,4 @@
-use email_encoding::headers::EmailWriter;
+use email_encoding::headers::writer::EmailWriter;
 
 use super::{Header, HeaderName, HeaderValue};
 use crate::{
@@ -31,7 +31,7 @@ macro_rules! mailbox_header {
                 let mut encoded_value = String::new();
                 let line_len = $header_name.len() + ": ".len();
                 {
-                    let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false, false);
+                    let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false);
                     self.0.encode(&mut w).expect("writing `Mailbox` returned an error");
                 }
 
@@ -81,7 +81,7 @@ macro_rules! mailboxes_header {
                 let mut encoded_value = String::new();
                 let line_len = $header_name.len() + ": ".len();
                 {
-                    let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false, false);
+                    let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false);
                     self.0.encode(&mut w).expect("writing `Mailboxes` returned an error");
                 }
 
@@ -110,7 +110,7 @@ mailbox_header! {
 
     `Sender` header
 
-    This header contains [`Mailbox`][self::Mailbox] associated with sender.
+    This header contains [`Mailbox`] associated with sender.
 
     ```no_test
     header::Sender("Mr. Sender <sender@example.com>".parse().unwrap())
@@ -124,7 +124,7 @@ mailboxes_header! {
 
     `From` header
 
-    This header contains [`Mailboxes`][self::Mailboxes].
+    This header contains [`Mailboxes`].
 
      */
     (From, "From")
@@ -135,7 +135,7 @@ mailboxes_header! {
 
     `Reply-To` header
 
-    This header contains [`Mailboxes`][self::Mailboxes].
+    This header contains [`Mailboxes`].
 
      */
     (ReplyTo, "Reply-To")
@@ -146,7 +146,7 @@ mailboxes_header! {
 
     `To` header
 
-    This header contains [`Mailboxes`][self::Mailboxes].
+    This header contains [`Mailboxes`].
 
      */
     (To, "To")
@@ -157,7 +157,7 @@ mailboxes_header! {
 
     `Cc` header
 
-    This header contains [`Mailboxes`][self::Mailboxes].
+    This header contains [`Mailboxes`].
 
      */
     (Cc, "Cc")
@@ -168,7 +168,7 @@ mailboxes_header! {
 
     `Bcc` header
 
-    This header contains [`Mailboxes`][self::Mailboxes].
+    This header contains [`Mailboxes`].
 
      */
     (Bcc, "Bcc")
@@ -252,7 +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)));
@@ -265,7 +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)));
@@ -281,7 +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())));
@@ -297,7 +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())));
@@ -306,14 +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())));
@@ -324,9 +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

@@ -7,7 +7,7 @@ use std::{
     ops::Deref,
 };
 
-use email_encoding::headers::EmailWriter;
+use email_encoding::headers::writer::EmailWriter;
 
 pub use self::{
     content::*,
@@ -66,7 +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> {
@@ -124,22 +124,18 @@ impl Headers {
     }
 
     pub(crate) fn find_header(&self, name: &str) -> Option<&HeaderValue> {
-        self.headers
-            .iter()
-            .find(|value| name.eq_ignore_ascii_case(&value.name))
+        self.headers.iter().find(|value| name == value.name)
     }
 
     fn find_header_mut(&mut self, name: &str) -> Option<&mut HeaderValue> {
-        self.headers
-            .iter_mut()
-            .find(|value| name.eq_ignore_ascii_case(&value.name))
+        self.headers.iter_mut().find(|value| name == value.name)
     }
 
     fn find_header_index(&self, name: &str) -> Option<usize> {
         self.headers
             .iter()
             .enumerate()
-            .find(|(_i, value)| name.eq_ignore_ascii_case(&value.name))
+            .find(|(_i, value)| name == value.name)
             .map(|(i, _)| i)
     }
 }
@@ -161,18 +157,9 @@ impl Display for Headers {
 /// A possible error when converting a `HeaderName` from another type.
 // comes from `http` crate
 #[allow(missing_copy_implementations)]
-#[derive(Clone)]
-pub struct InvalidHeaderName {
-    _priv: (),
-}
-
-impl fmt::Debug for InvalidHeaderName {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("InvalidHeaderName")
-            // skip _priv noise
-            .finish()
-    }
-}
+#[derive(Debug, Clone)]
+#[non_exhaustive]
+pub struct InvalidHeaderName;
 
 impl fmt::Display for InvalidHeaderName {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -189,14 +176,11 @@ pub struct HeaderName(Cow<'static, str>);
 impl HeaderName {
     /// Creates a new header name
     pub fn new_from_ascii(ascii: String) -> Result<Self, InvalidHeaderName> {
-        if !ascii.is_empty()
-            && ascii.len() <= 76
-            && ascii.is_ascii()
-            && !ascii.contains(|c| c == ':' || c == ' ')
+        if !ascii.is_empty() && ascii.len() <= 76 && ascii.is_ascii() && !ascii.contains([':', ' '])
         {
             Ok(Self(Cow::Owned(ascii)))
         } else {
-            Err(InvalidHeaderName { _priv: () })
+            Err(InvalidHeaderName)
         }
     }
 
@@ -257,23 +241,19 @@ impl AsRef<str> for HeaderName {
 
 impl PartialEq<HeaderName> for HeaderName {
     fn eq(&self, other: &HeaderName) -> bool {
-        let s1: &str = self.as_ref();
-        let s2: &str = other.as_ref();
-        s1 == s2
+        self.eq_ignore_ascii_case(other)
     }
 }
 
 impl PartialEq<&str> for HeaderName {
     fn eq(&self, other: &&str) -> bool {
-        let s: &str = self.as_ref();
-        s == *other
+        self.eq_ignore_ascii_case(other)
     }
 }
 
 impl PartialEq<HeaderName> for &str {
     fn eq(&self, other: &HeaderName) -> bool {
-        let s: &str = other.as_ref();
-        *self == s
+        self.eq_ignore_ascii_case(other)
     }
 }
 
@@ -310,7 +290,7 @@ impl HeaderValue {
     /// acceptable for use if `encoded_value` contains only ascii
     /// printable characters and is already line folded.
     ///
-    /// When in doubt use [`HeaderValue::new`].
+    /// When in doubt, use [`HeaderValue::new`].
     pub fn dangerous_new_pre_encoded(
         name: HeaderName,
         raw_value: String,
@@ -348,7 +328,7 @@ impl<'a> HeaderValueEncoder<'a> {
 
     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);
+        let writer = EmailWriter::new(writer, line_len, 0, false);
 
         Self {
             writer,
@@ -435,7 +415,7 @@ mod tests {
 
     #[test]
     fn empty_headername() {
-        assert!(HeaderName::new_from_ascii(String::from("")).is_err());
+        assert!(HeaderName::new_from_ascii("".to_owned()).is_err());
     }
 
     #[test]
@@ -467,6 +447,60 @@ mod tests {
         let _ = HeaderName::new_from_ascii_str("");
     }
 
+    #[test]
+    fn headername_headername_eq() {
+        assert_eq!(
+            HeaderName::new_from_ascii_str("From"),
+            HeaderName::new_from_ascii_str("From")
+        );
+    }
+
+    #[test]
+    fn headername_str_eq() {
+        assert_eq!(HeaderName::new_from_ascii_str("From"), "From");
+    }
+
+    #[test]
+    fn str_headername_eq() {
+        assert_eq!("From", HeaderName::new_from_ascii_str("From"));
+    }
+
+    #[test]
+    fn headername_headername_eq_case_insensitive() {
+        assert_eq!(
+            HeaderName::new_from_ascii_str("From"),
+            HeaderName::new_from_ascii_str("from")
+        );
+    }
+
+    #[test]
+    fn headername_str_eq_case_insensitive() {
+        assert_eq!(HeaderName::new_from_ascii_str("From"), "from");
+    }
+
+    #[test]
+    fn str_headername_eq_case_insensitive() {
+        assert_eq!("from", HeaderName::new_from_ascii_str("From"));
+    }
+
+    #[test]
+    fn headername_headername_ne() {
+        assert_ne!(
+            HeaderName::new_from_ascii_str("From"),
+            HeaderName::new_from_ascii_str("To")
+        );
+    }
+
+    #[test]
+    fn headername_str_ne() {
+        assert_ne!(HeaderName::new_from_ascii_str("From"), "To");
+    }
+
+    #[test]
+    fn str_headername_ne() {
+        assert_ne!("From", HeaderName::new_from_ascii_str("To"));
+    }
+
     // names taken randomly from https://it.wikipedia.org/wiki/Pinco_Pallino
 
     #[test]
@@ -474,7 +508,7 @@ 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!(
@@ -488,7 +522,7 @@ 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!(
@@ -506,7 +540,7 @@ 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!(
@@ -525,7 +559,7 @@ 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!(
@@ -543,7 +577,7 @@ 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!(
@@ -557,7 +591,7 @@ 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!(
@@ -571,7 +605,7 @@ 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!(
@@ -609,20 +643,17 @@ mod tests {
         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(),
+            "🌍 <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",
+                " =?utf-8?b?SsSBbmlzIELEk3J6acWGxaE=?= <janis@example.com>, =?utf-8?b?U2U=?=\r\n",
+                " =?utf-8?b?w6FuIMOTIFJ1ZGHDrQ==?= <sean@example.com>\r\n",
             )
         );
     }
@@ -633,7 +664,7 @@ mod tests {
         headers.insert_raw(
             HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳".to_string(),)
+            "🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳".to_owned(),)
         );
 
         assert_eq!(
@@ -654,7 +685,7 @@ 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!(
@@ -669,27 +700,24 @@ 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!(
@@ -699,8 +727,8 @@ mod tests {
                 "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",
+                " =?utf-8?b?SsSBbmlzIELEk3J6acWGxaE=?= <janis@example.com>, =?utf-8?b?U2U=?=\r\n",
+                " =?utf-8?b?w6FuIMOTIFJ1ZGHDrQ==?= <sean@example.com>\r\n",
                 "From: Someone <somewhere@example.com>\r\n",
                 "Content-Transfer-Encoding: quoted-printable\r\n",
             )
@@ -712,7 +740,7 @@ 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!(

src/message/header/special.rs

@@ -91,14 +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

@@ -125,7 +125,7 @@ mod test {
         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 +1,36 @@
+//! Partial parsers implementation of [RFC2234]: Augmented BNF for
+//! Syntax Specifications: ABNF.
+//!
+//! [RFC2234]: https://datatracker.ietf.org/doc/html/rfc2234
+
+use nom::{
+    branch::alt,
+    character::complete::{char, satisfy},
+    IResult, Parser,
+};
+
+// 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(input: &str) -> IResult<&str, char> {
+    satisfy(|c| c.is_ascii_alphabetic()).parse(input)
+}
+
+// DIGIT          =  %x30-39
+//                        ; 0-9
+pub(super) fn digit(input: &str) -> IResult<&str, char> {
+    satisfy(|c| c.is_ascii_digit()).parse(input)
+}
+
+// DQUOTE         =  %x22
+//                        ; " (Double Quote)
+pub(super) fn dquote(input: &str) -> IResult<&str, char> {
+    char('"').parse(input)
+}
+
+// WSP            =  SP / HTAB
+//                        ; white space
+pub(super) fn wsp(input: &str) -> IResult<&str, char> {
+    alt((char(' '), char('\t'))).parse(input)
+}

src/message/mailbox/parsers/rfc2822.rs

@@ -0,0 +1,340 @@
+//! Partial parsers implementation of [RFC2822]: Internet Message
+//! Format.
+//!
+//! [RFC2822]: https://datatracker.ietf.org/doc/html/rfc2822
+
+use nom::{
+    branch::alt,
+    character::complete::{char, satisfy},
+    combinator::{eof, map, opt},
+    multi::{fold_many0, fold_many1, many0, many1, separated_list0},
+    sequence::{delimited, pair, preceded, terminated},
+    IResult, Parser,
+};
+
+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(input: &str) -> IResult<&str, char> {
+    satisfy(|c| matches!(u32::from(c), 1..=8 | 11 | 12 | 14..=31 | 127)).parse(input)
+}
+
+// text            =       %d1-9 /         ; Characters excluding CR and LF
+//                         %d11 /
+//                         %d12 /
+//                         %d14-127 /
+//                         obs-text
+fn text(input: &str) -> IResult<&str, char> {
+    satisfy(|c| matches!(u32::from(c), 1..=9 | 11 | 12 | 14..=127)).parse(input)
+}
+
+// 3.2.2. Quoted characters
+// https://datatracker.ietf.org/doc/html/rfc2822#section-3.2.2
+
+// quoted-pair     =       ("\" text) / obs-qp
+fn quoted_pair(input: &str) -> IResult<&str, char> {
+    preceded(char('\\'), text).parse(input)
+}
+
+// 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(super) fn fws(input: &str) -> IResult<&str, Option<char>> {
+    map(
+        pair(opt(rfc2234::wsp), many0(rfc2234::wsp)),
+        |(first, _rest)| first,
+    )
+    .parse(input)
+}
+
+// CFWS            =       *([FWS] comment) (([FWS] comment) / FWS)
+pub(super) fn cfws(input: &str) -> IResult<&str, Option<char>> {
+    // TODO: comment are not currently supported, so for now a cfws is
+    // the same as a fws.
+    fws(input)
+}
+
+// 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.
+//                         "$" / "%" /     ;  Used for atoms
+//                         "&" / "'" /
+//                         "*" / "+" /
+//                         "-" / "/" /
+//                         "=" / "?" /
+//                         "^" / "_" /
+//                         "`" / "{" /
+//                         "|" / "}" /
+//                         "~"
+pub(super) fn atext(input: &str) -> IResult<&str, char> {
+    alt((
+        rfc2234::alpha,
+        rfc2234::digit,
+        satisfy(|c| {
+            matches!(
+                c,
+                '!' | '#'
+                    | '$'
+                    | '%'
+                    | '&'
+                    | '\''
+                    | '*'
+                    | '+'
+                    | '-'
+                    | '/'
+                    | '='
+                    | '?'
+                    | '^'
+                    | '_'
+                    | '`'
+                    | '{'
+                    | '|'
+                    | '}'
+                    | '~'
+            )
+        }),
+        // also allow non ASCII UTF8 chars
+        rfc5336::utf8_non_ascii,
+    ))
+    .parse(input)
+}
+
+// atom            =       [CFWS] 1*atext [CFWS]
+pub(super) fn atom(input: &str) -> IResult<&str, String> {
+    map(
+        pair(
+            cfws,
+            fold_many1(atext, String::new, |mut acc, c| {
+                acc.push(c);
+                acc
+            }),
+        ),
+        |(cfws, mut chars)| {
+            if let Some(cfws) = cfws {
+                chars.insert(0, cfws);
+            }
+            chars
+        },
+    )
+    .parse(input)
+}
+
+// dot-atom        =       [CFWS] dot-atom-text [CFWS]
+pub(super) fn dot_atom(input: &str) -> IResult<&str, String> {
+    map(pair(cfws, dot_atom_text), |(_cfws, text)| text).parse(input)
+}
+
+// dot-atom-text   =       1*atext *("." 1*atext)
+pub(super) fn dot_atom_text(input: &str) -> IResult<&str, String> {
+    map(
+        pair(
+            fold_many1(atext, String::new, |mut acc, c| {
+                acc.push(c);
+                acc
+            }),
+            many0(map(
+                pair(
+                    char('.'),
+                    fold_many1(atext, String::new, |mut acc, c| {
+                        acc.push(c);
+                        acc
+                    }),
+                ),
+                |(dot, chars)| format!("{dot}{chars}"),
+            )),
+        ),
+        |(first, rest)| {
+            let mut result = first;
+            for part in rest {
+                result.push_str(&part);
+            }
+            result
+        },
+    )
+    .parse(input)
+}
+
+// 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(input: &str) -> IResult<&str, char> {
+    alt((
+        satisfy(|c| matches!(u32::from(c), 33 | 35..=91 | 93..=126)),
+        no_ws_ctl,
+    ))
+    .parse(input)
+}
+
+// qcontent        =       qtext / quoted-pair
+pub(super) fn qcontent(input: &str) -> IResult<&str, char> {
+    alt((qtext, quoted_pair, rfc5336::utf8_non_ascii)).parse(input)
+}
+
+// quoted-string   =       [CFWS]
+//                         DQUOTE *([FWS] qcontent) [FWS] DQUOTE
+//                         [CFWS]
+fn quoted_string(input: &str) -> IResult<&str, String> {
+    map(
+        delimited(
+            rfc2234::dquote,
+            fold_many0(
+                map(pair(fws, qcontent), |(_fws, c)| c),
+                String::new,
+                |mut acc, c| {
+                    acc.push(c);
+                    acc
+                },
+            ),
+            preceded(many0(satisfy(char::is_whitespace)), rfc2234::dquote),
+        ),
+        |s| s,
+    )
+    .parse(input)
+}
+
+// 3.2.6. Miscellaneous tokens
+// https://datatracker.ietf.org/doc/html/rfc2822#section-3.2.6
+
+// word            =       atom / quoted-string
+fn word(input: &str) -> IResult<&str, String> {
+    alt((quoted_string, atom)).parse(input)
+}
+
+// phrase          =       1*word / obs-phrase
+fn phrase(input: &str) -> IResult<&str, String> {
+    alt((obs_phrase, map(many1(word), |words| words.join(" ")))).parse(input)
+}
+
+// 3.4. Address Specification
+// https://datatracker.ietf.org/doc/html/rfc2822#section-3.4
+
+// mailbox         =       name-addr / addr-spec
+pub(crate) fn mailbox(input: &str) -> IResult<&str, (Option<String>, (String, String))> {
+    terminated(alt((name_addr, map(addr_spec, |addr| (None, addr)))), eof).parse(input)
+}
+
+// name-addr       =       [display-name] angle-addr
+fn name_addr(input: &str) -> IResult<&str, (Option<String>, (String, String))> {
+    pair(opt(display_name), angle_addr).parse(input)
+}
+
+// angle-addr      =       [CFWS] "<" addr-spec ">" [CFWS] / obs-angle-addr
+fn angle_addr(input: &str) -> IResult<&str, (String, String)> {
+    delimited((cfws, char('<')), addr_spec, (char('>'), cfws)).parse(input)
+}
+
+// display-name    =       phrase
+fn display_name(input: &str) -> IResult<&str, String> {
+    phrase(input)
+}
+
+// mailbox-list    =       (mailbox *("," mailbox)) / obs-mbox-list
+#[allow(clippy::type_complexity)]
+pub(crate) fn mailbox_list(input: &str) -> IResult<&str, Vec<(Option<String>, (String, String))>> {
+    terminated(
+        separated_list0(
+            delimited(
+                many0(satisfy(char::is_whitespace)),
+                char(','),
+                many0(satisfy(char::is_whitespace)),
+            ),
+            alt((name_addr, map(addr_spec, |addr| (None, addr)))),
+        ),
+        eof,
+    )
+    .parse(input)
+}
+
+// 3.4.1. Addr-spec specification
+// https://datatracker.ietf.org/doc/html/rfc2822#section-3.4.1
+
+// addr-spec       =       local-part "@" domain
+pub(super) fn addr_spec(input: &str) -> IResult<&str, (String, String)> {
+    pair(terminated(local_part, char('@')), domain).parse(input)
+}
+
+// local-part      =       dot-atom / quoted-string / obs-local-part
+pub(super) fn local_part(input: &str) -> IResult<&str, String> {
+    alt((dot_atom, quoted_string, obs_local_part)).parse(input)
+}
+
+// domain          =       dot-atom / domain-literal / obs-domain
+pub(super) fn domain(input: &str) -> IResult<&str, String> {
+    // NOTE: omitting domain-literal since it may never be used
+    alt((dot_atom, obs_domain)).parse(input)
+}
+
+// 4.1. Miscellaneous obsolete tokens
+// https://datatracker.ietf.org/doc/html/rfc2822#section-4.1
+
+// obs-phrase      =       word *(word / "." / CFWS)
+fn obs_phrase(input: &str) -> IResult<&str, String> {
+    // NOTE: the CFWS is already captured by the word, no need to add
+    // it there.
+    map(
+        pair(word, many0(alt((word, map(char('.'), |c| c.to_string()))))),
+        |(first, rest)| {
+            let mut result = first;
+            for part in rest {
+                result.push_str(&part);
+            }
+            result
+        },
+    )
+    .parse(input)
+}
+
+// 4.4. Obsolete Addressing
+// https://datatracker.ietf.org/doc/html/rfc2822#section-4.4
+
+// obs-local-part  =       word *("." word)
+pub(super) fn obs_local_part(input: &str) -> IResult<&str, String> {
+    map(
+        pair(
+            word,
+            many0(map(pair(char('.'), word), |(dot, w)| format!("{dot}{w}"))),
+        ),
+        |(first, rest)| {
+            let mut result = first;
+            for part in rest {
+                result.push_str(&part);
+            }
+            result
+        },
+    )
+    .parse(input)
+}
+
+// obs-domain      =       atom *("." atom)
+pub(super) fn obs_domain(input: &str) -> IResult<&str, String> {
+    map(
+        pair(
+            atom,
+            many0(map(pair(char('.'), atom), |(dot, a)| format!("{dot}{a}"))),
+        ),
+        |(first, rest)| {
+            let mut result = first;
+            for part in rest {
+                result.push_str(&part);
+            }
+            result
+        },
+    )
+    .parse(input)
+}

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 nom::{character::complete::satisfy, IResult, Parser};
+
+// 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(input: &str) -> IResult<&str, char> {
+    satisfy(|c| c.len_utf8() > 1).parse(input)
+}

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)
     }
 }
 
@@ -36,7 +36,7 @@ impl<'de> Deserialize<'de> for Mailbox {
             {
                 struct FieldVisitor;
 
-                impl<'de> Visitor<'de> for FieldVisitor {
+                impl Visitor<'_> for FieldVisitor {
                     type Value = Field;
 
                     fn expecting(&self, formatter: &mut Formatter<'_>) -> FmtResult {
@@ -111,7 +111,7 @@ impl Serialize for Mailboxes {
     where
         S: Serializer,
     {
-        serializer.serialize_str(&self.to_string())
+        serializer.collect_str(self)
     }
 }
 
@@ -179,7 +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());
     }
@@ -198,7 +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()
         );
@@ -211,7 +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 +5,16 @@ use std::{
     str::FromStr,
 };
 
-use email_encoding::headers::EmailWriter;
+use email_encoding::headers::writer::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 +71,7 @@ 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.optional_breakpoint();
+            w.space();
             w.write_char('<')?;
         }
 
@@ -86,7 +87,7 @@ 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 +109,24 @@ 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 (_rest, (name, (user, domain))) = parsers::mailbox(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 +134,7 @@ 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>);
 
@@ -188,7 +173,7 @@ impl Mailboxes {
         self
     }
 
-    /// Adds a new [`Mailbox`] to the list, in a Vec::push style pattern.
+    /// Adds a new [`Mailbox`] to the list, in a `Vec::push` style pattern.
     ///
     /// # Examples
     ///
@@ -275,7 +260,7 @@ impl Mailboxes {
         for mailbox in self.iter() {
             if !mem::take(&mut first) {
                 w.write_char(',')?;
-                w.optional_breakpoint();
+                w.space();
             }
 
             mailbox.encode(w)?;
@@ -356,34 +341,16 @@ 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 (_rest, parsed_mailboxes) = parsers::mailbox_list(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))
@@ -436,7 +403,7 @@ 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)
 }
 
@@ -476,8 +443,6 @@ fn write_quoted_string_char(f: &mut Formatter<'_>, c: char) -> FmtResult {
 
 #[cfg(test)]
 mod test {
-    use std::convert::TryInto;
-
     use pretty_assertions::assert_eq;
 
     use super::Mailbox;
@@ -565,7 +530,7 @@ mod test {
         assert_eq!(
             format!(
                 "{}",
-                Mailbox::new(Some("".into()), "kayo@example.com".parse().unwrap())
+                Mailbox::new(Some("".to_owned()), "kayo@example.com".parse().unwrap())
             ),
             "kayo@example.com"
         );
@@ -590,6 +555,14 @@ mod test {
         );
     }
 
+    #[test]
+    fn parse_address_only_trim() {
+        assert_eq!(
+            " kayo@example.com ".parse(),
+            Ok(Mailbox::new(None, "kayo@example.com".parse().unwrap()))
+        );
+    }
+
     #[test]
     fn parse_address_with_name() {
         assert_eq!(
@@ -601,6 +574,17 @@ mod test {
         );
     }
 
+    #[test]
+    fn parse_address_with_name_trim() {
+        assert_eq!(
+            " K. <kayo@example.com> ".parse(),
+            Ok(Mailbox::new(
+                Some("K.".into()),
+                "kayo@example.com".parse().unwrap()
+            ))
+        );
+    }
+
     #[test]
     fn parse_address_with_empty_name() {
         assert_eq!(
@@ -612,7 +596,7 @@ mod test {
     #[test]
     fn parse_address_with_empty_name_trim() {
         assert_eq!(
-            " <kayo@example.com>".parse(),
+            " <kayo@example.com> ".parse(),
             Ok(Mailbox::new(None, "kayo@example.com".parse().unwrap()))
         );
     }
@@ -620,7 +604,7 @@ 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
@@ -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 {
@@ -396,12 +406,20 @@ 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;
 
     #[test]
     fn single_part_binary() {

src/message/mod.rs

@@ -277,7 +277,7 @@ impl MessageBuilder {
     /// Shortcut for `self.date(SystemTime::now())`, it is automatically inserted
     /// if no date has been provided.
     pub fn date_now(self) -> Self {
-        self.date(SystemTime::now())
+        self.date(crate::time::now())
     }
 
     /// Set or add mailbox to `ReplyTo` header
@@ -345,9 +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
@@ -388,13 +388,13 @@ impl MessageBuilder {
 
     /// Keep the `Bcc` header
     ///
-    /// By default the `Bcc` header is removed from the email after
+    /// 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 behaviour.
+    /// Calling this method overrides the default behavior.
     pub fn keep_bcc(mut self) -> Self {
         self.drop_bcc = false;
         self
@@ -457,12 +457,12 @@ impl MessageBuilder {
         self.build(MessageBody::Raw(body.into_vec()))
     }
 
-    /// Create message using mime body ([`MultiPart`][self::MultiPart])
+    /// Create message using mime body ([`MultiPart`])
     pub fn multipart(self, part: MultiPart) -> Result<Message, EmailError> {
         self.mime_1_0().build(MessageBody::Mime(Part::Multi(part)))
     }
 
-    /// Create message using mime body ([`SinglePart`][self::SinglePart])
+    /// Create message using mime body ([`SinglePart`])
     pub fn singlepart(self, part: SinglePart) -> Result<Message, EmailError> {
         self.mime_1_0().build(MessageBody::Mime(Part::Single(part)))
     }
@@ -503,6 +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
@@ -520,9 +525,9 @@ 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");
         out
     }
@@ -532,7 +537,10 @@ impl Message {
     /// Example:
     /// ```rust
     /// use lettre::{
-    ///     message::dkim::{DkimConfig, DkimSigningAlgorithm, DkimSigningKey},
+    ///     message::{
+    ///         dkim::{DkimConfig, DkimSigningAlgorithm, DkimSigningKey},
+    ///         header::ContentType,
+    ///     },
     ///     Message,
     /// };
     ///
@@ -541,7 +549,8 @@ 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())
+    ///     .header(ContentType::TEXT_PLAIN)
+    ///     .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
@@ -572,8 +581,8 @@ impl Message {
     /// -----END RSA PRIVATE KEY-----";
     /// 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!(
@@ -596,7 +605,7 @@ impl EmailFormat for Message {
             MessageBody::Mime(p) => p.format(out),
             MessageBody::Raw(r) => {
                 out.extend_from_slice(b"\r\n");
-                out.extend_from_slice(r)
+                out.extend_from_slice(r);
             }
         }
     }
@@ -630,7 +639,7 @@ 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())
@@ -760,7 +769,7 @@ mod test {
                 continue;
             }
 
-            assert_eq!(line.0, line.1)
+            assert_eq!(line.0, line.1);
         }
     }
 

src/rustls_crypto.rs

@@ -0,0 +1,14 @@
+use std::sync::Arc;
+
+use rustls::crypto::CryptoProvider;
+
+pub(crate) fn crypto_provider() -> Arc<CryptoProvider> {
+    CryptoProvider::get_default().cloned().unwrap_or_else(|| {
+        #[cfg(feature = "aws-lc-rs")]
+        let provider = rustls::crypto::aws_lc_rs::default_provider();
+        #[cfg(not(feature = "aws-lc-rs"))]
+        let provider = rustls::crypto::ring::default_provider();
+
+        Arc::new(provider)
+    })
+}

src/time.rs

@@ -0,0 +1,26 @@
+use std::time::SystemTime;
+
+#[cfg(all(feature = "web", target_arch = "wasm32"))]
+pub(crate) fn now() -> SystemTime {
+    fn to_std_systemtime(time: web_time::SystemTime) -> std::time::SystemTime {
+        let duration = time
+            .duration_since(web_time::SystemTime::UNIX_EPOCH)
+            .unwrap();
+        SystemTime::UNIX_EPOCH + duration
+    }
+
+    // FIXME: change to:
+    // #[allow(
+    //     clippy::disallowed_methods,
+    //     reason = "`web-time` aliases `std::time::SystemTime::now` on non-WASM platforms"
+    // )]
+    #[allow(clippy::disallowed_methods)]
+    to_std_systemtime(web_time::SystemTime::now())
+}
+
+#[cfg(not(all(feature = "web", target_arch = "wasm32")))]
+pub(crate) fn now() -> SystemTime {
+    // FIXME: change to #[expect(clippy::disallowed_methods, reason = "the `web` feature is disabled")]
+    #[allow(clippy::disallowed_methods)]
+    SystemTime::now()
+}

src/transport/file/error.rs

@@ -34,6 +34,7 @@ impl Error {
 
     /// Returns true if the error is an envelope serialization or deserialization error
     #[cfg(feature = "file-transport-envelope")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "file-transport-envelope")))]
     pub fn is_envelope(&self) -> bool {
         matches!(self.inner.kind, Kind::Envelope)
     }
@@ -54,7 +55,7 @@ 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);
         }
 
@@ -68,9 +69,9 @@ impl fmt::Display for Error {
             Kind::Io => f.write_str("response error")?,
             #[cfg(feature = "file-transport-envelope")]
             Kind::Envelope => f.write_str("internal client error")?,
-        };
+        }
 
-        if let Some(ref e) = self.inner.source {
+        if let Some(e) = &self.inner.source {
             write!(f, ": {e}")?;
         }
 

src/transport/file/mod.rs

@@ -11,7 +11,7 @@
 //! # fn main() -> Result<(), Box<dyn Error>> {
 //! use std::env::temp_dir;
 //!
-//! use lettre::{FileTransport, Message, Transport};
+//! use lettre::{message::header::ContentType, FileTransport, Message, Transport};
 //!
 //! // Write to the local temp directory
 //! let sender = FileTransport::new(temp_dir());
@@ -20,10 +20,10 @@
 //!     .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!"))?;
 //!
-//! let result = sender.send(&email);
-//! assert!(result.is_ok());
+//! sender.send(&email)?;
 //! # Ok(())
 //! # }
 //!
@@ -44,7 +44,7 @@
 //! # fn main() -> Result<(), Box<dyn Error>> {
 //! use std::env::temp_dir;
 //!
-//! use lettre::{FileTransport, Message, Transport};
+//! use lettre::{message::header::ContentType, FileTransport, Message, Transport};
 //!
 //! // Write to the local temp directory
 //! let sender = FileTransport::with_envelope(temp_dir());
@@ -53,10 +53,10 @@
 //!     .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!"))?;
 //!
-//! let result = sender.send(&email);
-//! assert!(result.is_ok());
+//! sender.send(&email)?;
 //! # Ok(())
 //! # }
 //!
@@ -73,7 +73,9 @@
 //! # async fn run() -> Result<(), Box<dyn Error>> {
 //! use std::env::temp_dir;
 //!
-//! use lettre::{AsyncFileTransport, AsyncTransport, Message, Tokio1Executor};
+//! use lettre::{
+//!     message::header::ContentType, AsyncFileTransport, AsyncTransport, Message, Tokio1Executor,
+//! };
 //!
 //! // Write to the local temp directory
 //! let sender = AsyncFileTransport::<Tokio1Executor>::new(temp_dir());
@@ -82,10 +84,10 @@
 //!     .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!"))?;
 //!
-//! let result = sender.send(email).await;
-//! assert!(result.is_ok());
+//! sender.send(email).await?;
 //! # Ok(())
 //! # }
 //! ```
@@ -99,7 +101,10 @@
 //! # async fn run() -> Result<(), Box<dyn Error>> {
 //! use std::env::temp_dir;
 //!
-//! use lettre::{AsyncFileTransport, AsyncStd1Executor, AsyncTransport, Message};
+//! use lettre::{
+//!     message::header::ContentType, AsyncFileTransport, AsyncStd1Executor, AsyncTransport,
+//!     Message,
+//! };
 //!
 //! // Write to the local temp directory
 //! let sender = AsyncFileTransport::<AsyncStd1Executor>::new(temp_dir());
@@ -108,10 +113,10 @@
 //!     .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!"))?;
 //!
-//! let result = sender.send(email).await;
-//! assert!(result.is_ok());
+//! sender.send(email).await?;
 //! # Ok(())
 //! # }
 //! ```
@@ -125,6 +130,7 @@
 //! Reply-To: Yuin <yuin@domain.tld>
 //! To: Hei <hei@domain.tld>
 //! Subject: Happy new year
+//! Content-Type: text/plain; charset=utf-8
 //! Date: Tue, 18 Aug 2020 22:50:17 GMT
 //!
 //! Be happy!
@@ -157,7 +163,7 @@ 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 {
@@ -193,6 +199,7 @@ impl FileTransport {
     /// Writes the email content in eml format and the envelope
     /// in json format.
     #[cfg(feature = "file-transport-envelope")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "file-transport-envelope")))]
     pub fn with_envelope<P: AsRef<Path>>(path: P) -> FileTransport {
         FileTransport {
             path: PathBuf::from(path.as_ref()),
@@ -205,6 +212,7 @@ impl FileTransport {
     ///
     /// Reads the envelope and the raw message content.
     #[cfg(feature = "file-transport-envelope")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "file-transport-envelope")))]
     pub fn read(&self, email_id: &str) -> Result<(Envelope, Vec<u8>), Error> {
         use std::fs;
 
@@ -243,6 +251,7 @@ where
     /// Writes the email content in eml format and the envelope
     /// in json format.
     #[cfg(feature = "file-transport-envelope")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "file-transport-envelope")))]
     pub fn with_envelope<P: AsRef<Path>>(path: P) -> Self {
         Self {
             inner: FileTransport::with_envelope(path),
@@ -254,6 +263,7 @@ where
     ///
     /// Reads the envelope and the raw message content.
     #[cfg(feature = "file-transport-envelope")]
+    #[cfg_attr(docsrs, doc(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!("{email_id}.eml"));
         let eml = E::fs_read(&eml_file).await.map_err(error::io)?;
@@ -266,6 +276,16 @@ where
     }
 }
 
+#[cfg(any(feature = "async-std1", feature = "tokio1"))]
+impl<E: Executor> Clone for AsyncFileTransport<E> {
+    fn clone(&self) -> Self {
+        Self {
+            inner: self.inner.clone(),
+            marker_: PhantomData,
+        }
+    }
+}
+
 impl Transport for FileTransport {
     type Ok = Id;
     type Error = Error;

src/transport/mod.rs

@@ -12,7 +12,7 @@
 //!
 //! * a service from your Cloud or hosting provider
 //! * an email server ([MTA] for Mail Transfer Agent, like Postfix or Exchange), running either
-//! locally on your servers or accessible over the network
+//!   locally on your servers or accessible over the network
 //! * a dedicated external service, like Mailchimp, Mailgun, etc.
 //!
 //! In most cases, the best option is to:
@@ -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
 //!
@@ -56,16 +56,20 @@
 //! #
 //! # #[cfg(all(feature = "builder", feature = "smtp-transport"))]
 //! # fn main() -> Result<(), Box<dyn Error>> {
-//! use lettre::{transport::smtp::authentication::Credentials, Message, SmtpTransport, Transport};
+//! use lettre::{
+//!     message::header::ContentType, transport::smtp::authentication::Credentials, Message,
+//!     SmtpTransport, Transport,
+//! };
 //!
 //! let email = Message::builder()
 //!     .from("NoBody <nobody@domain.tld>".parse()?)
 //!     .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!"))?;
 //!
-//! 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 +79,7 @@
 //! // 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 +101,7 @@
 //! [`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;
@@ -135,6 +140,10 @@ pub trait Transport {
     }
 
     fn send_raw(&self, envelope: &Envelope, email: &[u8]) -> Result<Self::Ok, Self::Error>;
+
+    /// Shuts down the transport. Future calls to [`Self::send`] and
+    /// [`Self::send_raw`] might fail.
+    fn shutdown(&self) {}
 }
 
 /// Async Transport method for emails
@@ -161,4 +170,8 @@ pub trait AsyncTransport {
     }
 
     async fn send_raw(&self, envelope: &Envelope, email: &[u8]) -> Result<Self::Ok, Self::Error>;
+
+    /// Shuts down the transport. Future calls to [`Self::send`] and
+    /// [`Self::send_raw`] might fail.
+    async fn shutdown(&self) {}
 }

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);
         }
 
@@ -65,9 +65,9 @@ impl fmt::Display for Error {
         match self.inner.kind {
             Kind::Response => f.write_str("response error")?,
             Kind::Client => f.write_str("internal client error")?,
-        };
+        }
 
-        if let Some(ref e) = self.inner.source {
+        if let Some(e) = &self.inner.source {
             write!(f, ": {e}")?;
         }
 

src/transport/sendmail/mod.rs

@@ -7,18 +7,18 @@
 //! #
 //! # #[cfg(all(feature = "sendmail-transport", feature = "builder"))]
 //! # fn main() -> Result<(), Box<dyn Error>> {
-//! use lettre::{Message, SendmailTransport, Transport};
+//! use lettre::{message::header::ContentType, Message, SendmailTransport, Transport};
 //!
 //! let email = Message::builder()
 //!     .from("NoBody <nobody@domain.tld>".parse()?)
 //!     .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!"))?;
 //!
 //! let sender = SendmailTransport::new();
-//! let result = sender.send(&email);
-//! assert!(result.is_ok());
+//! sender.send(&email)?;
 //! # Ok(())
 //! # }
 //!
@@ -34,7 +34,8 @@
 //! # #[cfg(all(feature = "tokio1", feature = "sendmail-transport", feature = "builder"))]
 //! # async fn run() -> Result<(), Box<dyn Error>> {
 //! use lettre::{
-//!     AsyncSendmailTransport, AsyncTransport, Message, SendmailTransport, Tokio1Executor,
+//!     message::header::ContentType, AsyncSendmailTransport, AsyncTransport, Message,
+//!     SendmailTransport, Tokio1Executor,
 //! };
 //!
 //! let email = Message::builder()
@@ -42,11 +43,11 @@
 //!     .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!"))?;
 //!
 //! let sender = AsyncSendmailTransport::<Tokio1Executor>::new();
-//! let result = sender.send(email).await;
-//! assert!(result.is_ok());
+//! sender.send(email).await?;
 //! # Ok(())
 //! # }
 //! ```
@@ -58,18 +59,17 @@
 //! #
 //! # #[cfg(all(feature = "async-std1", feature = "sendmail-transport", feature = "builder"))]
 //! # async fn run() -> Result<(), Box<dyn Error>> {
-//! use lettre::{Message, AsyncTransport, AsyncStd1Executor, AsyncSendmailTransport};
+//! use lettre::{Message, AsyncTransport, AsyncStd1Executor,message::header::ContentType, AsyncSendmailTransport};
 //!
 //! let email = Message::builder()
 //!     .from("NoBody <nobody@domain.tld>".parse()?)
 //!     .reply_to("Yuin <yuin@domain.tld>".parse()?)
 //!     .to("Hei <hei@domain.tld>".parse()?)
-//!     .subject("Happy new year")
+//!     .subject("Happy new year").header(ContentType::TEXT_PLAIN)
 //!     .body(String::from("Be happy!"))?;
 //!
 //! let sender = AsyncSendmailTransport::<AsyncStd1Executor>::new();
-//! let result = sender.send(email).await;
-//! assert!(result.is_ok());
+//! sender.send(email).await?;
 //! # Ok(())
 //! # }
 //! ```
@@ -120,7 +120,7 @@ impl SendmailTransport {
     /// Creates a new transport with the `sendmail` command
     ///
     /// Note: This uses the `sendmail` command in the current `PATH`. To use another command,
-    /// use [SendmailTransport::new_with_command].
+    /// use [`SendmailTransport::new_with_command`].
     pub fn new() -> SendmailTransport {
         SendmailTransport {
             command: DEFAULT_SENDMAIL.into(),
@@ -157,7 +157,7 @@ where
     /// Creates a new transport with the `sendmail` command
     ///
     /// Note: This uses the `sendmail` command in the current `PATH`. To use another command,
-    /// use [AsyncSendmailTransport::new_with_command].
+    /// use [`AsyncSendmailTransport::new_with_command`].
     pub fn new() -> Self {
         Self {
             inner: SendmailTransport::new(),

src/transport/smtp/async_transport.rs

@@ -12,6 +12,12 @@ use async_trait::async_trait;
 use super::pool::async_impl::Pool;
 #[cfg(feature = "pool")]
 use super::PoolConfig;
+#[cfg(any(
+    feature = "tokio1-native-tls",
+    feature = "tokio1-rustls",
+    feature = "async-std1-rustls"
+))]
+use super::Tls;
 use super::{
     client::AsyncSmtpConnection, ClientId, Credentials, Error, Mechanism, Response, SmtpInfo,
 };
@@ -24,6 +30,30 @@ use crate::Tokio1Executor;
 use crate::{Envelope, Executor};
 
 /// Asynchronously sends emails using the SMTP protocol
+///
+/// `AsyncSmtpTransport` is the primary way for communicating
+/// with SMTP relay servers to send email messages. It holds the
+/// client connect configuration and creates new connections
+/// as necessary.
+///
+/// # Connection pool
+///
+/// When the `pool` feature is enabled (default), `AsyncSmtpTransport` maintains a
+/// connection pool to manage SMTP connections. The pool:
+///
+/// - Establishes a new connection when sending a message.
+/// - Recycles connections internally after a message is sent.
+/// - Reuses connections for subsequent messages, reducing connection setup overhead.
+///
+/// The connection pool can grow to hold multiple SMTP connections if multiple
+/// emails are sent concurrently, as SMTP does not support multiplexing within a
+/// single connection.
+///
+/// However, **connection reuse is not possible** if the `SyncSmtpTransport` instance
+/// is dropped after every email send operation. You must reuse the instance
+/// of this struct for the connection pool to be of any use.
+///
+/// To customize connection pool settings, use [`AsyncSmtpTransportBuilder::pool_config`].
 #[cfg_attr(docsrs, doc(cfg(any(feature = "tokio1", feature = "async-std1"))))]
 pub struct AsyncSmtpTransport<E: Executor> {
     #[cfg(feature = "pool")]
@@ -45,10 +75,15 @@ impl AsyncTransport for AsyncSmtpTransport<Tokio1Executor> {
         let result = conn.send(envelope, email).await?;
 
         #[cfg(not(feature = "pool"))]
-        conn.quit().await?;
+        conn.abort().await;
 
         Ok(result)
     }
+
+    async fn shutdown(&self) {
+        #[cfg(feature = "pool")]
+        self.inner.shutdown().await;
+    }
 }
 
 #[cfg(feature = "async-std1")]
@@ -67,6 +102,11 @@ impl AsyncTransport for AsyncSmtpTransport<AsyncStd1Executor> {
 
         Ok(result)
     }
+
+    async fn shutdown(&self) {
+        #[cfg(feature = "pool")]
+        self.inner.shutdown().await;
+    }
 }
 
 impl<E> AsyncSmtpTransport<E>
@@ -81,16 +121,15 @@ where
     /// to validate TLS certificates.
     #[cfg(any(
         feature = "tokio1-native-tls",
-        feature = "tokio1-rustls-tls",
-        feature = "async-std1-native-tls",
-        feature = "async-std1-rustls-tls"
+        feature = "tokio1-rustls",
+        feature = "async-std1-rustls"
     ))]
     #[cfg_attr(
         docsrs,
         doc(cfg(any(
             feature = "tokio1-native-tls",
-            feature = "tokio1-rustls-tls",
-            feature = "async-std1-rustls-tls"
+            feature = "tokio1-rustls",
+            feature = "async-std1-rustls"
         )))
     )]
     pub fn relay(relay: &str) -> Result<AsyncSmtpTransportBuilder, Error> {
@@ -103,7 +142,7 @@ 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.
@@ -116,16 +155,15 @@ where
     /// or emails will be sent to the server, protecting from downgrade attacks.
     #[cfg(any(
         feature = "tokio1-native-tls",
-        feature = "tokio1-rustls-tls",
-        feature = "async-std1-native-tls",
-        feature = "async-std1-rustls-tls"
+        feature = "tokio1-rustls",
+        feature = "async-std1-rustls"
     ))]
     #[cfg_attr(
         docsrs,
         doc(cfg(any(
             feature = "tokio1-native-tls",
-            feature = "tokio1-rustls-tls",
-            feature = "async-std1-rustls-tls"
+            feature = "tokio1-rustls",
+            feature = "async-std1-rustls"
         )))
     )]
     pub fn starttls_relay(relay: &str) -> Result<AsyncSmtpTransportBuilder, Error> {
@@ -151,28 +189,128 @@ 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, port and EHLO name can be provided
+    /// in a single URL. This may be simpler than having to configure SMTP
+    /// through multiple configuration parameters and then having to pass
+    /// those options to lettre.
+    ///
+    /// The URL is created in the following way:
+    /// `scheme://user:pass@hostname:port/ehlo-name?tls=TLS`.
+    ///
+    /// `user` (Username) and `pass` (Password) are optional in case the
+    /// SMTP relay doesn't require authentication. When `port` is not
+    /// configured it is automatically determined based on the `scheme`.
+    /// `ehlo-name` optionally overwrites the hostname sent for the EHLO
+    /// command. `TLS` controls whether STARTTLS is simply enabled
+    /// (`opportunistic` - not enough to prevent man-in-the-middle attacks)
+    /// or `required` (require the server to upgrade the connection to
+    /// STARTTLS, otherwise fail on suspicion of main-in-the-middle attempt).
+    ///
+    /// Use the following table to construct your SMTP url:
+    ///
+    /// | scheme  | `tls` query parameter | example                                            | default port | remarks                                                                                                                               |
+    /// | ------- | --------------------- | -------------------------------------------------- | ------------ | ------------------------------------------------------------------------------------------------------------------------------------- |
+    /// | `smtps` | unset                 | `smtps://user:pass@hostname:port`                  | 465          | SMTP over TLS, recommended method                                                                                                     |
+    /// | `smtp`  | `required`            | `smtp://user:pass@hostname:port?tls=required`      | 587          | SMTP with STARTTLS required, when SMTP over TLS is not available                                                                      |
+    /// | `smtp`  | `opportunistic`       | `smtp://user:pass@hostname:port?tls=opportunistic` | 587          | SMTP with optionally STARTTLS when supported by the server. Not suitable for production use: vulnerable to a man-in-the-middle attack |
+    /// | `smtp`  | unset                 | `smtp://user:pass@hostname:port`                   | 587          | Always unencrypted SMTP. Not suitable for production use: sends all data unencrypted                                                  |
+    ///
+    /// IMPORTANT: some parameters like `user` and `pass` cannot simply
+    /// be concatenated to construct the final URL because special characters
+    /// contained within the parameter may confuse the URL decoder.
+    /// Manually URL encode the parameters before concatenating them or use
+    /// a proper URL encoder, like the following cargo script:
+    ///
+    /// ```rust
+    /// # const TOML: &str = r#"
+    /// #!/usr/bin/env cargo
+    ///
+    /// //! ```cargo
+    /// //! [dependencies]
+    /// //! url = "2"
+    /// //! ```
+    /// # "#;
+    ///
+    /// use url::Url;
+    ///
+    /// fn main() {
+    ///     // don't touch this line
+    ///     let mut url = Url::parse("foo://bar").unwrap();
+    ///
+    ///     // configure the scheme (`smtp` or `smtps`) here.
+    ///     url.set_scheme("smtps").unwrap();
+    ///     // configure the username and password.
+    ///     // remove the following two lines if unauthenticated.
+    ///     url.set_username("username").unwrap();
+    ///     url.set_password(Some("password")).unwrap();
+    ///     // configure the hostname
+    ///     url.set_host(Some("smtp.example.com")).unwrap();
+    ///     // configure the port - only necessary if using a non-default port
+    ///     url.set_port(Some(465)).unwrap();
+    ///     // configure the EHLO name
+    ///     url.set_path("ehlo-name");
+    ///
+    ///     println!("{url}");
+    /// }
+    /// ```
+    ///
+    /// The connection URL can then be used in the following way:
+    ///
+    /// ```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",
+    ///     )?
+    ///     .build();
+    ///
+    /// // Send the email
+    /// mailer.send(email).await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls", 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?;
 
@@ -219,13 +357,27 @@ 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;
         self
     }
 
-    /// Set the authentication mechanism to use
+    /// Set the authentication credentials to use
     pub fn credentials(mut self, credentials: Credentials) -> Self {
         self.info.credentials = Some(credentials);
         self
@@ -238,6 +390,17 @@ impl AsyncSmtpTransportBuilder {
     }
 
     /// Set the port to use
+    ///
+    /// # ⚠️⚠️⚠️ You probably don't need to call this method ⚠️⚠️⚠️
+    ///
+    /// lettre usually picks the correct `port` when building
+    /// [`AsyncSmtpTransport`] using [`AsyncSmtpTransport::relay`] or
+    /// [`AsyncSmtpTransport::starttls_relay`].
+    ///
+    /// # Errors
+    ///
+    /// Using the incorrect `port` and [`Self::tls`] combination may
+    /// lead to hard to debug IO errors coming from the TLS library.
     pub fn port(mut self, port: u16) -> Self {
         self.info.port = port;
         self
@@ -250,21 +413,31 @@ impl AsyncSmtpTransportBuilder {
     }
 
     /// Set the TLS settings to use
+    ///
+    /// # ⚠️⚠️⚠️ You probably don't need to call this method ⚠️⚠️⚠️
+    ///
+    /// By default lettre chooses the correct `tls` configuration when
+    /// building [`AsyncSmtpTransport`] using [`AsyncSmtpTransport::relay`] or
+    /// [`AsyncSmtpTransport::starttls_relay`].
+    ///
+    /// # Errors
+    ///
+    /// Using the incorrect [`Tls`] and [`Self::port`] combination may
+    /// lead to hard to debug IO errors coming from the TLS library.
     #[cfg(any(
         feature = "tokio1-native-tls",
-        feature = "tokio1-rustls-tls",
-        feature = "async-std1-native-tls",
-        feature = "async-std1-rustls-tls"
+        feature = "tokio1-rustls",
+        feature = "async-std1-rustls"
     ))]
     #[cfg_attr(
         docsrs,
         doc(cfg(any(
             feature = "tokio1-native-tls",
-            feature = "tokio1-rustls-tls",
-            feature = "async-std1-rustls-tls"
+            feature = "tokio1-rustls",
+            feature = "async-std1-rustls"
         )))
     )]
-    pub fn tls(mut self, tls: super::Tls) -> Self {
+    pub fn tls(mut self, tls: Tls) -> Self {
         self.info.tls = tls;
         self
     }
@@ -297,7 +470,7 @@ impl AsyncSmtpTransportBuilder {
 }
 
 /// Build client
-pub struct AsyncSmtpClient<E> {
+pub(super) struct AsyncSmtpClient<E> {
     info: SmtpInfo,
     marker_: PhantomData<E>,
 }
@@ -309,7 +482,7 @@ where
     /// Creates a new connection directly usable to send emails
     ///
     /// Handles encryption and authentication
-    pub async fn connection(&self) -> Result<AsyncSmtpConnection, Error> {
+    pub(super) async fn connection(&self) -> Result<AsyncSmtpConnection, Error> {
         let mut conn = E::connect(
             &self.info.server,
             self.info.port,

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,
@@ -98,11 +98,17 @@ impl Mechanism {
                 let decoded_challenge = challenge
                     .ok_or_else(|| error::client("This mechanism does expect a challenge"))?;
 
-                if ["User Name", "Username:", "Username"].contains(&decoded_challenge) {
+                if contains_ignore_ascii_case(
+                    decoded_challenge,
+                    ["User Name", "Username:", "Username", "User Name\0"],
+                ) {
                     return Ok(credentials.authentication_identity.clone());
                 }
 
-                if ["Password", "Password:"].contains(&decoded_challenge) {
+                if contains_ignore_ascii_case(
+                    decoded_challenge,
+                    ["Password", "Password:", "Password\0"],
+                ) {
                     return Ok(credentials.secret.clone());
                 }
 
@@ -119,6 +125,15 @@ impl Mechanism {
     }
 }
 
+fn contains_ignore_ascii_case<'a>(
+    haystack: &str,
+    needles: impl IntoIterator<Item = &'a str>,
+) -> bool {
+    needles
+        .into_iter()
+        .any(|item| item.eq_ignore_ascii_case(haystack))
+}
+
 #[cfg(test)]
 mod test {
     use super::{Credentials, Mechanism};
@@ -127,7 +142,7 @@ 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 +155,7 @@ 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(),
@@ -153,13 +168,30 @@ mod test {
         assert!(mechanism.response(&credentials, None).is_err());
     }
 
+    #[test]
+    fn test_login_case_insensitive() {
+        let mechanism = Mechanism::Login;
+
+        let credentials = Credentials::new("alice".to_owned(), "wonderland".to_owned());
+
+        assert_eq!(
+            mechanism.response(&credentials, Some("username")).unwrap(),
+            "alice"
+        );
+        assert_eq!(
+            mechanism.response(&credentials, Some("password")).unwrap(),
+            "wonderland"
+        );
+        assert!(mechanism.response(&credentials, None).is_err());
+    }
+
     #[test]
     fn test_xoauth2() {
         let mechanism = Mechanism::Xoauth2;
 
         let credentials = Credentials::new(
-            "username".to_string(),
-            "vF9dft4qmTc2Nvb3RlckBhdHRhdmlzdGEuY29tCg==".to_string(),
+            "username".to_owned(),
+            "vF9dft4qmTc2Nvb3RlckBhdHRhdmlzdGEuY29tCg==".to_owned(),
         );
 
         assert_eq!(
@@ -172,7 +204,7 @@ 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

@@ -6,7 +6,8 @@ use futures_util::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
 use super::async_net::AsyncTokioStream;
 #[cfg(feature = "tracing")]
 use super::escape_crlf;
-use super::{AsyncNetworkStream, ClientCodec, TlsParameters};
+#[allow(deprecated)]
+use super::{async_net::AsyncNetworkStream, ClientCodec, TlsParameters};
 use crate::{
     transport::smtp::{
         authentication::{Credentials, Mechanism},
@@ -35,6 +36,7 @@ macro_rules! try_smtp (
 pub struct AsyncSmtpConnection {
     /// TCP stream between client and server
     /// Value is None before connection
+    #[allow(deprecated)]
     stream: BufReader<AsyncNetworkStream>,
     /// Panic state
     panic: bool,
@@ -52,18 +54,48 @@ impl AsyncSmtpConnection {
     ///
     /// Sends EHLO and parses server information
     #[cfg(feature = "tokio1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "tokio1")))]
     pub async fn connect_with_transport(
         stream: Box<dyn AsyncTokioStream>,
         hello_name: &ClientId,
     ) -> Result<AsyncSmtpConnection, Error> {
+        #[allow(deprecated)]
         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?;
+    /// # Ok(())
+    /// # }
+    /// ```
     #[cfg(feature = "tokio1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "tokio1")))]
     pub async fn connect_tokio1<T: tokio1_crate::net::ToSocketAddrs>(
         server: T,
         timeout: Option<Duration>,
@@ -71,6 +103,7 @@ impl AsyncSmtpConnection {
         tls_parameters: Option<TlsParameters>,
         local_address: Option<IpAddr>,
     ) -> Result<AsyncSmtpConnection, Error> {
+        #[allow(deprecated)]
         let stream =
             AsyncNetworkStream::connect_tokio1(server, timeout, tls_parameters, local_address)
                 .await?;
@@ -81,16 +114,19 @@ impl AsyncSmtpConnection {
     ///
     /// Sends EHLO and parses server information
     #[cfg(feature = "async-std1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async-std1")))]
     pub async fn connect_asyncstd1<T: async_std::net::ToSocketAddrs>(
         server: T,
         timeout: Option<Duration>,
         hello_name: &ClientId,
         tls_parameters: Option<TlsParameters>,
     ) -> Result<AsyncSmtpConnection, Error> {
+        #[allow(deprecated)]
         let stream = AsyncNetworkStream::connect_asyncstd1(server, timeout, tls_parameters).await?;
         Self::connect_impl(stream, hello_name).await
     }
 
+    #[allow(deprecated)]
     async fn connect_impl(
         stream: AsyncNetworkStream,
         hello_name: &ClientId,
@@ -132,7 +168,7 @@ 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(
@@ -172,6 +208,12 @@ impl AsyncSmtpConnection {
         !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,
@@ -212,6 +254,7 @@ impl AsyncSmtpConnection {
     }
 
     /// Sets the underlying stream
+    #[allow(deprecated)]
     pub fn set_stream(&mut self, stream: AsyncNetworkStream) {
         self.stream = BufReader::new(stream);
     }
@@ -226,7 +269,7 @@ 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],
@@ -335,8 +378,36 @@ impl AsyncSmtpConnection {
     }
 
     /// The X509 certificate of the server (DER encoded)
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
+    )]
     pub fn peer_certificate(&self) -> Result<Vec<u8>, Error> {
         self.stream.get_ref().peer_certificate()
     }
+
+    /// Currently this is only avaialable when using Boring TLS and
+    /// returns the result of the verification of the TLS certificate
+    /// presented by the peer, if any. Only the last error encountered
+    /// during verification is presented.
+    /// It can be useful when you don't want to fail outright the TLS
+    /// negotiation, for example when a self-signed certificate is
+    /// encountered, but still want to record metrics or log the fact.
+    /// When using DANE verification, the PKI root of trust moves from
+    /// the CAs to DNS, so self-signed certificates are permitted as long
+    /// as the TLSA records match the leaf or issuer certificates.
+    /// It cannot be called on non Boring TLS streams.
+    #[cfg(feature = "boring-tls")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "boring-tls")))]
+    pub fn tls_verify_result(&self) -> Result<(), Error> {
+        self.stream.get_ref().tls_verify_result()
+    }
+
+    /// All the X509 certificates of the chain (DER encoded)
+    #[cfg(any(feature = "rustls", feature = "boring-tls"))]
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "rustls", feature = "boring-tls"))))]
+    pub fn certificate_chain(&self) -> Result<Vec<Vec<u8>>, Error> {
+        self.stream.get_ref().certificate_chain()
+    }
 }

src/transport/smtp/client/async_net.rs

@@ -6,16 +6,16 @@ use std::{
     time::Duration,
 };
 
-#[cfg(feature = "async-std1-native-tls")]
-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,
+    AsyncRead as FuturesAsyncRead, AsyncWrite as FuturesAsyncWrite, Error as IoError,
     Result as IoResult,
 };
-#[cfg(feature = "async-std1-rustls-tls")]
-use futures_rustls::client::TlsStream as AsyncStd1RustlsTlsStream;
+#[cfg(feature = "async-std1-rustls")]
+use futures_rustls::client::TlsStream as AsyncStd1RustlsStream;
+#[cfg(any(feature = "tokio1-rustls", feature = "async-std1-rustls"))]
+use rustls::pki_types::ServerName;
 #[cfg(feature = "tokio1-boring-tls")]
 use tokio1_boring::SslStream as Tokio1SslStream;
 #[cfg(feature = "tokio1")]
@@ -27,15 +27,14 @@ use tokio1_crate::net::{
 };
 #[cfg(feature = "tokio1-native-tls")]
 use tokio1_native_tls_crate::TlsStream as Tokio1TlsStream;
-#[cfg(feature = "tokio1-rustls-tls")]
-use tokio1_rustls::client::TlsStream as Tokio1RustlsTlsStream;
+#[cfg(feature = "tokio1-rustls")]
+use tokio1_rustls::client::TlsStream as Tokio1RustlsStream;
 
 #[cfg(any(
     feature = "tokio1-native-tls",
-    feature = "tokio1-rustls-tls",
+    feature = "tokio1-rustls",
     feature = "tokio1-boring-tls",
-    feature = "async-std1-native-tls",
-    feature = "async-std1-rustls-tls"
+    feature = "async-std1-rustls"
 ))]
 use super::InnerTlsParameters;
 use super::TlsParameters;
@@ -45,6 +44,10 @@ use crate::transport::smtp::{error, Error};
 
 /// A network stream
 #[derive(Debug)]
+#[deprecated(
+    since = "0.11.14",
+    note = "This struct was not meant to be made public"
+)]
 pub struct AsyncNetworkStream {
     inner: InnerAsyncNetworkStream,
 }
@@ -75,8 +78,8 @@ enum InnerAsyncNetworkStream {
     #[cfg(feature = "tokio1-native-tls")]
     Tokio1NativeTls(Tokio1TlsStream<Box<dyn AsyncTokioStream>>),
     /// Encrypted Tokio 1.x TCP stream
-    #[cfg(feature = "tokio1-rustls-tls")]
-    Tokio1RustlsTls(Tokio1RustlsTlsStream<Box<dyn AsyncTokioStream>>),
+    #[cfg(feature = "tokio1-rustls")]
+    Tokio1Rustls(Tokio1RustlsStream<Box<dyn AsyncTokioStream>>),
     /// Encrypted Tokio 1.x TCP stream
     #[cfg(feature = "tokio1-boring-tls")]
     Tokio1BoringTls(Tokio1SslStream<Box<dyn AsyncTokioStream>>),
@@ -84,15 +87,13 @@ enum InnerAsyncNetworkStream {
     #[cfg(feature = "async-std1")]
     AsyncStd1Tcp(AsyncStd1TcpStream),
     /// Encrypted Tokio 1.x TCP stream
-    #[cfg(feature = "async-std1-native-tls")]
-    AsyncStd1NativeTls(AsyncStd1TlsStream<AsyncStd1TcpStream>),
-    /// Encrypted Tokio 1.x TCP stream
-    #[cfg(feature = "async-std1-rustls-tls")]
-    AsyncStd1RustlsTls(AsyncStd1RustlsTlsStream<AsyncStd1TcpStream>),
+    #[cfg(feature = "async-std1-rustls")]
+    AsyncStd1Rustls(AsyncStd1RustlsStream<AsyncStd1TcpStream>),
     /// Can't be built
     None,
 }
 
+#[allow(deprecated)]
 impl AsyncNetworkStream {
     fn new(inner: InnerAsyncNetworkStream) -> Self {
         if let InnerAsyncNetworkStream::None = inner {
@@ -104,27 +105,24 @@ impl AsyncNetworkStream {
 
     /// 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(),
+            #[cfg(feature = "tokio1-rustls")]
+            InnerAsyncNetworkStream::Tokio1Rustls(s) => s.get_ref().0.peer_addr(),
             #[cfg(feature = "tokio1-boring-tls")]
-            InnerAsyncNetworkStream::Tokio1BoringTls(ref s) => s.get_ref().peer_addr(),
+            InnerAsyncNetworkStream::Tokio1BoringTls(s) => s.get_ref().peer_addr(),
             #[cfg(feature = "async-std1")]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(ref s) => s.peer_addr(),
-            #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(ref s) => s.get_ref().peer_addr(),
-            #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(ref s) => s.get_ref().0.peer_addr(),
+            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => s.peer_addr(),
+            #[cfg(feature = "async-std1-rustls")]
+            InnerAsyncNetworkStream::AsyncStd1Rustls(s) => s.get_ref().0.peer_addr(),
             InnerAsyncNetworkStream::None => {
                 debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
-                Err(IoError::new(
-                    ErrorKind::Other,
+                Err(IoError::other(
                     "InnerAsyncNetworkStream::None must never be built",
                 ))
             }
@@ -132,11 +130,13 @@ impl AsyncNetworkStream {
     }
 
     #[cfg(feature = "tokio1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "tokio1")))]
     pub fn use_existing_tokio1(stream: Box<dyn AsyncTokioStream>) -> AsyncNetworkStream {
         AsyncNetworkStream::new(InnerAsyncNetworkStream::Tokio1Tcp(stream))
     }
 
     #[cfg(feature = "tokio1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "tokio1")))]
     pub async fn connect_tokio1<T: Tokio1ToSocketAddrs>(
         server: T,
         timeout: Option<Duration>,
@@ -176,7 +176,7 @@ impl AsyncNetworkStream {
                             last_err = Some(io::Error::new(
                                 io::ErrorKind::TimedOut,
                                 "connection timed out",
-                            ))
+                            ));
                         }
                     }
                 } else {
@@ -203,14 +203,15 @@ impl AsyncNetworkStream {
     }
 
     #[cfg(feature = "async-std1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async-std1")))]
     pub async fn connect_asyncstd1<T: AsyncStd1ToSocketAddrs>(
         server: T,
         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
+        // 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
-        // connected which is a blocking operation.
+        // been connected, which is a blocking operation.
         async fn try_connect_timeout<T: AsyncStd1ToSocketAddrs>(
             server: T,
             timeout: Duration,
@@ -228,7 +229,7 @@ impl AsyncNetworkStream {
                         last_err = Some(io::Error::new(
                             io::ErrorKind::TimedOut,
                             "connection timed out",
-                        ))
+                        ));
                     }
                 }
             }
@@ -259,26 +260,25 @@ impl AsyncNetworkStream {
                 feature = "tokio1",
                 not(any(
                     feature = "tokio1-native-tls",
-                    feature = "tokio1-rustls-tls",
+                    feature = "tokio1-rustls",
                     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");
+                panic!("Trying to upgrade an AsyncNetworkStream without having enabled either the tokio1-native-tls or the tokio1-rustls feature");
             }
 
             #[cfg(any(
                 feature = "tokio1-native-tls",
-                feature = "tokio1-rustls-tls",
+                feature = "tokio1-rustls",
                 feature = "tokio1-boring-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!(),
+                let InnerAsyncNetworkStream::Tokio1Tcp(tcp_stream) = tcp_stream else {
+                    unreachable!()
                 };
 
                 self.inner = Self::upgrade_tokio1_tls(tcp_stream, tls_parameters)
@@ -286,22 +286,18 @@ impl AsyncNetworkStream {
                     .map_err(error::connection)?;
                 Ok(())
             }
-            #[cfg(all(
-                feature = "async-std1",
-                not(any(feature = "async-std1-native-tls", feature = "async-std1-rustls-tls"))
-            ))]
+            #[cfg(all(feature = "async-std1", not(feature = "async-std1-rustls")))]
             InnerAsyncNetworkStream::AsyncStd1Tcp(_) => {
                 let _ = tls_parameters;
-                panic!("Trying to upgrade an AsyncNetworkStream without having enabled either the async-std1-native-tls or the async-std1-rustls-tls feature");
+                panic!("Trying to upgrade an AsyncNetworkStream without having enabled the async-std1-rustls feature");
             }
 
-            #[cfg(any(feature = "async-std1-native-tls", feature = "async-std1-rustls-tls"))]
+            #[cfg(feature = "async-std1-rustls")]
             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!(),
+                let InnerAsyncNetworkStream::AsyncStd1Tcp(tcp_stream) = tcp_stream else {
+                    unreachable!()
                 };
 
                 self.inner = Self::upgrade_asyncstd1_tls(tcp_stream, tls_parameters)
@@ -316,18 +312,18 @@ impl AsyncNetworkStream {
     #[allow(unused_variables)]
     #[cfg(any(
         feature = "tokio1-native-tls",
-        feature = "tokio1-rustls-tls",
+        feature = "tokio1-rustls",
         feature = "tokio1-boring-tls"
     ))]
     async fn upgrade_tokio1_tls(
         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")]
-            InnerTlsParameters::NativeTls(connector) => {
+            InnerTlsParameters::NativeTls { connector } => {
                 #[cfg(not(feature = "tokio1-native-tls"))]
                 panic!("built without the tokio1-native-tls feature");
 
@@ -343,14 +339,13 @@ impl AsyncNetworkStream {
                     Ok(InnerAsyncNetworkStream::Tokio1NativeTls(stream))
                 };
             }
-            #[cfg(feature = "rustls-tls")]
-            InnerTlsParameters::RustlsTls(config) => {
-                #[cfg(not(feature = "tokio1-rustls-tls"))]
-                panic!("built without the tokio1-rustls-tls feature");
+            #[cfg(feature = "rustls")]
+            InnerTlsParameters::Rustls { config } => {
+                #[cfg(not(feature = "tokio1-rustls"))]
+                panic!("built without the tokio1-rustls feature");
 
-                #[cfg(feature = "tokio1-rustls-tls")]
+                #[cfg(feature = "tokio1-rustls")]
                 return {
-                    use rustls::ServerName;
                     use tokio1_rustls::TlsConnector;
 
                     let domain = ServerName::try_from(domain.as_str())
@@ -358,21 +353,24 @@ 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))
+                    Ok(InnerAsyncNetworkStream::Tokio1Rustls(stream))
                 };
             }
             #[cfg(feature = "boring-tls")]
-            InnerTlsParameters::BoringTls(connector) => {
+            InnerTlsParameters::BoringTls {
+                connector,
+                accept_invalid_hostnames,
+            } => {
                 #[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);
+                    config.set_verify_hostname(accept_invalid_hostnames);
 
                     let stream = tokio1_boring::connect(config, &domain, tcp_stream)
                         .await
@@ -384,11 +382,7 @@ impl AsyncNetworkStream {
     }
 
     #[allow(unused_variables)]
-    #[cfg(any(
-        feature = "async-std1-native-tls",
-        feature = "async-std1-rustls-tls",
-        feature = "async-std1-boring-tls"
-    ))]
+    #[cfg(feature = "async-std1-rustls")]
     async fn upgrade_asyncstd1_tls(
         tcp_stream: AsyncStd1TcpStream,
         mut tls_parameters: TlsParameters,
@@ -397,73 +391,122 @@ impl AsyncNetworkStream {
 
         match tls_parameters.connector {
             #[cfg(feature = "native-tls")]
-            InnerTlsParameters::NativeTls(connector) => {
+            InnerTlsParameters::NativeTls { connector } => {
                 panic!("native-tls isn't supported with async-std yet. See https://github.com/lettre/lettre/pull/531#issuecomment-757893531");
-
-                /*
-                #[cfg(not(feature = "async-std1-native-tls"))]
-                panic!("built without the async-std1-native-tls feature");
-
-                #[cfg(feature = "async-std1-native-tls")]
-                return {
-                    use async_native_tls::TlsConnector;
-
-                    // TODO: fix
-                    let connector: TlsConnector = todo!();
-                    // let connector = TlsConnector::from(connector);
-                    let stream = connector.connect(&domain, tcp_stream).await?;
-                    Ok(InnerAsyncNetworkStream::AsyncStd1NativeTls(stream))
-                };
-                */
             }
-            #[cfg(feature = "rustls-tls")]
-            InnerTlsParameters::RustlsTls(config) => {
-                #[cfg(not(feature = "async-std1-rustls-tls"))]
-                panic!("built without the async-std1-rustls-tls feature");
+            #[cfg(feature = "rustls")]
+            InnerTlsParameters::Rustls { config } => {
+                #[cfg(not(feature = "async-std1-rustls"))]
+                panic!("built without the async-std1-rustls feature");
 
-                #[cfg(feature = "async-std1-rustls-tls")]
+                #[cfg(feature = "async-std1-rustls")]
                 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))
+                    Ok(InnerAsyncNetworkStream::AsyncStd1Rustls(stream))
                 };
             }
             #[cfg(feature = "boring-tls")]
-            InnerTlsParameters::BoringTls(connector) => {
+            InnerTlsParameters::BoringTls { .. } => {
                 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-rustls")]
+            InnerAsyncNetworkStream::Tokio1Rustls(_) => 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,
+            #[cfg(feature = "async-std1-rustls")]
+            InnerAsyncNetworkStream::AsyncStd1Rustls(_) => true,
             InnerAsyncNetworkStream::None => false,
         }
     }
 
+    #[cfg(feature = "boring-tls")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "boring-tls")))]
+    pub fn tls_verify_result(&self) -> Result<(), Error> {
+        match &self.inner {
+            #[cfg(feature = "tokio1")]
+            InnerAsyncNetworkStream::Tokio1Tcp(_) => {
+                Err(error::client("Connection is not encrypted"))
+            }
+            #[cfg(feature = "tokio1-native-tls")]
+            InnerAsyncNetworkStream::Tokio1NativeTls(_) => panic!("Unsupported"),
+            #[cfg(feature = "tokio1-rustls")]
+            InnerAsyncNetworkStream::Tokio1Rustls(_) => panic!("Unsupported"),
+            #[cfg(feature = "tokio1-boring-tls")]
+            InnerAsyncNetworkStream::Tokio1BoringTls(stream) => {
+                stream.ssl().verify_result().map_err(error::tls)
+            }
+            #[cfg(feature = "async-std1")]
+            InnerAsyncNetworkStream::AsyncStd1Tcp(_) => {
+                Err(error::client("Connection is not encrypted"))
+            }
+            #[cfg(feature = "async-std1-rustls")]
+            InnerAsyncNetworkStream::AsyncStd1Rustls(_) => panic!("Unsupported"),
+            InnerAsyncNetworkStream::None => panic!("InnerNetworkStream::None must never be built"),
+        }
+    }
+
+    pub fn certificate_chain(&self) -> Result<Vec<Vec<u8>>, Error> {
+        match &self.inner {
+            #[cfg(feature = "tokio1")]
+            InnerAsyncNetworkStream::Tokio1Tcp(_) => {
+                Err(error::client("Connection is not encrypted"))
+            }
+            #[cfg(feature = "tokio1-native-tls")]
+            InnerAsyncNetworkStream::Tokio1NativeTls(_) => panic!("Unsupported"),
+            #[cfg(feature = "tokio1-rustls")]
+            InnerAsyncNetworkStream::Tokio1Rustls(stream) => Ok(stream
+                .get_ref()
+                .1
+                .peer_certificates()
+                .unwrap()
+                .iter()
+                .map(|c| c.to_vec())
+                .collect()),
+            #[cfg(feature = "tokio1-boring-tls")]
+            InnerAsyncNetworkStream::Tokio1BoringTls(stream) => Ok(stream
+                .ssl()
+                .peer_cert_chain()
+                .unwrap()
+                .iter()
+                .map(|c| c.to_der().map_err(error::tls))
+                .collect::<Result<Vec<_>, _>>()?),
+            #[cfg(feature = "async-std1")]
+            InnerAsyncNetworkStream::AsyncStd1Tcp(_) => {
+                Err(error::client("Connection is not encrypted"))
+            }
+            #[cfg(feature = "async-std1-rustls")]
+            InnerAsyncNetworkStream::AsyncStd1Rustls(stream) => Ok(stream
+                .get_ref()
+                .1
+                .peer_certificates()
+                .unwrap()
+                .iter()
+                .map(|c| c.to_vec())
+                .collect()),
+            InnerAsyncNetworkStream::None => panic!("InnerNetworkStream::None must never be built"),
+        }
+    }
+
     pub fn peer_certificate(&self) -> Result<Vec<u8>, Error> {
         match &self.inner {
             #[cfg(feature = "tokio1")]
@@ -478,16 +521,15 @@ impl AsyncNetworkStream {
                 .unwrap()
                 .to_der()
                 .map_err(error::tls)?),
-            #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(stream) => Ok(stream
+            #[cfg(feature = "tokio1-rustls")]
+            InnerAsyncNetworkStream::Tokio1Rustls(stream) => Ok(stream
                 .get_ref()
                 .1
                 .peer_certificates()
                 .unwrap()
                 .first()
                 .unwrap()
-                .clone()
-                .0),
+                .to_vec()),
             #[cfg(feature = "tokio1-boring-tls")]
             InnerAsyncNetworkStream::Tokio1BoringTls(stream) => Ok(stream
                 .ssl()
@@ -499,32 +541,30 @@ impl AsyncNetworkStream {
             InnerAsyncNetworkStream::AsyncStd1Tcp(_) => {
                 Err(error::client("Connection is not encrypted"))
             }
-            #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(t) => panic!("Unsupported"),
-            #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(stream) => Ok(stream
+            #[cfg(feature = "async-std1-rustls")]
+            InnerAsyncNetworkStream::AsyncStd1Rustls(stream) => Ok(stream
                 .get_ref()
                 .1
                 .peer_certificates()
                 .unwrap()
                 .first()
                 .unwrap()
-                .clone()
-                .0),
+                .to_vec()),
             InnerAsyncNetworkStream::None => panic!("InnerNetworkStream::None must never be built"),
         }
     }
 }
 
+#[allow(deprecated)]
 impl FuturesAsyncRead for AsyncNetworkStream {
     fn poll_read(
         mut self: Pin<&mut Self>,
         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())),
@@ -533,7 +573,7 @@ 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())),
@@ -541,8 +581,8 @@ impl FuturesAsyncRead for AsyncNetworkStream {
                     Poll::Pending => Poll::Pending,
                 }
             }
-            #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(ref mut s) => {
+            #[cfg(feature = "tokio1-rustls")]
+            InnerAsyncNetworkStream::Tokio1Rustls(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())),
@@ -551,7 +591,7 @@ impl FuturesAsyncRead for AsyncNetworkStream {
                 }
             }
             #[cfg(feature = "tokio1-boring-tls")]
-            InnerAsyncNetworkStream::Tokio1BoringTls(ref mut s) => {
+            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())),
@@ -560,15 +600,9 @@ impl FuturesAsyncRead for AsyncNetworkStream {
                 }
             }
             #[cfg(feature = "async-std1")]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(ref mut 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)
-            }
-            #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(ref mut s) => {
-                Pin::new(s).poll_read(cx, buf)
-            }
+            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => Pin::new(s).poll_read(cx, buf),
+            #[cfg(feature = "async-std1-rustls")]
+            InnerAsyncNetworkStream::AsyncStd1Rustls(s) => Pin::new(s).poll_read(cx, buf),
             InnerAsyncNetworkStream::None => {
                 debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
                 Poll::Ready(Ok(0))
@@ -577,31 +611,26 @@ impl FuturesAsyncRead for AsyncNetworkStream {
     }
 }
 
+#[allow(deprecated)]
 impl FuturesAsyncWrite for AsyncNetworkStream {
     fn poll_write(
         mut self: Pin<&mut Self>,
         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),
-            #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(ref mut s) => Pin::new(s).poll_write(cx, buf),
+            InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_write(cx, buf),
+            #[cfg(feature = "tokio1-rustls")]
+            InnerAsyncNetworkStream::Tokio1Rustls(s) => Pin::new(s).poll_write(cx, buf),
             #[cfg(feature = "tokio1-boring-tls")]
-            InnerAsyncNetworkStream::Tokio1BoringTls(ref mut s) => Pin::new(s).poll_write(cx, buf),
+            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),
-            #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(ref mut 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::AsyncStd1Tcp(s) => Pin::new(s).poll_write(cx, buf),
+            #[cfg(feature = "async-std1-rustls")]
+            InnerAsyncNetworkStream::AsyncStd1Rustls(s) => Pin::new(s).poll_write(cx, buf),
             InnerAsyncNetworkStream::None => {
                 debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
                 Poll::Ready(Ok(0))
@@ -610,21 +639,19 @@ impl FuturesAsyncWrite for AsyncNetworkStream {
     }
 
     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),
-            #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(ref mut s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_flush(cx),
+            #[cfg(feature = "tokio1-rustls")]
+            InnerAsyncNetworkStream::Tokio1Rustls(s) => Pin::new(s).poll_flush(cx),
             #[cfg(feature = "tokio1-boring-tls")]
-            InnerAsyncNetworkStream::Tokio1BoringTls(ref mut s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::Tokio1BoringTls(s) => Pin::new(s).poll_flush(cx),
             #[cfg(feature = "async-std1")]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(ref mut s) => Pin::new(s).poll_flush(cx),
-            #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(ref mut 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::AsyncStd1Tcp(s) => Pin::new(s).poll_flush(cx),
+            #[cfg(feature = "async-std1-rustls")]
+            InnerAsyncNetworkStream::AsyncStd1Rustls(s) => Pin::new(s).poll_flush(cx),
             InnerAsyncNetworkStream::None => {
                 debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
                 Poll::Ready(Ok(()))
@@ -633,21 +660,19 @@ impl FuturesAsyncWrite for AsyncNetworkStream {
     }
 
     fn poll_close(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_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),
-            #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(ref mut s) => Pin::new(s).poll_shutdown(cx),
+            InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_shutdown(cx),
+            #[cfg(feature = "tokio1-rustls")]
+            InnerAsyncNetworkStream::Tokio1Rustls(s) => Pin::new(s).poll_shutdown(cx),
             #[cfg(feature = "tokio1-boring-tls")]
-            InnerAsyncNetworkStream::Tokio1BoringTls(ref mut s) => Pin::new(s).poll_shutdown(cx),
+            InnerAsyncNetworkStream::Tokio1BoringTls(s) => Pin::new(s).poll_shutdown(cx),
             #[cfg(feature = "async-std1")]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(ref mut s) => Pin::new(s).poll_close(cx),
-            #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(ref mut 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::AsyncStd1Tcp(s) => Pin::new(s).poll_close(cx),
+            #[cfg(feature = "async-std1-rustls")]
+            InnerAsyncNetworkStream::AsyncStd1Rustls(s) => Pin::new(s).poll_close(cx),
             InnerAsyncNetworkStream::None => {
                 debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
                 Poll::Ready(Ok(()))

src/transport/smtp/client/connection.rs

@@ -100,7 +100,7 @@ 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(
@@ -143,7 +143,7 @@ impl SmtpConnection {
         hello_name: &ClientId,
     ) -> Result<(), Error> {
         if self.server_info.supports_feature(Extension::StartTls) {
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
             {
                 try_smtp!(self.command(Starttls), self);
                 self.stream.get_mut().upgrade_tls(tls_parameters)?;
@@ -153,11 +153,7 @@ impl SmtpConnection {
                 try_smtp!(self.ehlo(hello_name), self);
                 Ok(())
             }
-            #[cfg(not(any(
-                feature = "native-tls",
-                feature = "rustls-tls",
-                feature = "boring-tls"
-            )))]
+            #[cfg(not(any(feature = "native-tls", feature = "rustls", 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");
@@ -207,7 +203,7 @@ 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],
@@ -303,8 +299,36 @@ impl SmtpConnection {
     }
 
     /// The X509 certificate of the server (DER encoded)
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
+    )]
     pub fn peer_certificate(&self) -> Result<Vec<u8>, Error> {
         self.stream.get_ref().peer_certificate()
     }
+
+    /// Currently this is only avaialable when using Boring TLS and
+    /// returns the result of the verification of the TLS certificate
+    /// presented by the peer, if any. Only the last error encountered
+    /// during verification is presented.
+    /// It can be useful when you don't want to fail outright the TLS
+    /// negotiation, for example when a self-signed certificate is
+    /// encountered, but still want to record metrics or log the fact.
+    /// When using DANE verification, the PKI root of trust moves from
+    /// the CAs to DNS, so self-signed certificates are permitted as long
+    /// as the TLSA records match the leaf or issuer certificates.
+    /// It cannot be called on non Boring TLS streams.
+    #[cfg(feature = "boring-tls")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "boring-tls")))]
+    pub fn tls_verify_result(&self) -> Result<(), Error> {
+        self.stream.get_ref().tls_verify_result()
+    }
+
+    /// All the X509 certificates of the chain (DER encoded)
+    #[cfg(any(feature = "rustls", feature = "boring-tls"))]
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "rustls", feature = "boring-tls"))))]
+    pub fn certificate_chain(&self) -> Result<Vec<Vec<u8>>, Error> {
+        self.stream.get_ref().certificate_chain()
+    }
 }

src/transport/smtp/client/mod.rs

@@ -11,7 +11,7 @@
 //!     client::SmtpConnection, commands::*, extension::ClientId, SMTP_PORT,
 //! };
 //!
-//! let hello = ClientId::Domain("my_hostname".to_string());
+//! 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![]))?;
@@ -28,17 +28,18 @@ use std::fmt::Debug;
 #[cfg(any(feature = "tokio1", feature = "async-std1"))]
 pub use self::async_connection::AsyncSmtpConnection;
 #[cfg(any(feature = "tokio1", feature = "async-std1"))]
+#[allow(deprecated)]
 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", feature = "boring-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
 pub(super) use self::tls::InnerTlsParameters;
-#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
 pub use self::tls::TlsVersion;
 pub use self::{
     connection::SmtpConnection,
-    tls::{Certificate, Tls, TlsParameters, TlsParametersBuilder},
+    tls::{Certificate, CertificateStore, Identity, Tls, TlsParameters, TlsParametersBuilder},
 };
 
 #[cfg(any(feature = "tokio1", feature = "async-std1"))]
@@ -57,7 +58,7 @@ struct ClientCodec {
 
 impl ClientCodec {
     /// Creates a new client codec
-    pub fn new() -> Self {
+    pub(crate) fn new() -> Self {
         Self {
             status: CodecStatus::StartOfNewLine,
         }
@@ -139,7 +140,7 @@ mod test {
     }
 
     #[test]
-    #[cfg(feature = "log")]
+    #[cfg(feature = "tracing")]
     fn test_escape_crlf() {
         assert_eq!(escape_crlf("\r\n"), "<CRLF>");
         assert_eq!(escape_crlf("EHLO my_name\r\n"), "EHLO my_name<CRLF>");

src/transport/smtp/client/net.rs

@@ -1,4 +1,4 @@
-#[cfg(feature = "rustls-tls")]
+#[cfg(feature = "rustls")]
 use std::sync::Arc;
 use std::{
     io::{self, Read, Write},
@@ -11,11 +11,11 @@ use std::{
 use boring::ssl::SslStream;
 #[cfg(feature = "native-tls")]
 use native_tls::TlsStream;
-#[cfg(feature = "rustls-tls")]
-use rustls::{ClientConnection, ServerName, StreamOwned};
+#[cfg(feature = "rustls")]
+use rustls::{pki_types::ServerName, ClientConnection, StreamOwned};
 use socket2::{Domain, Protocol, Type};
 
-#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
 use super::InnerTlsParameters;
 use super::TlsParameters;
 use crate::transport::smtp::{error, Error};
@@ -36,8 +36,8 @@ enum InnerNetworkStream {
     #[cfg(feature = "native-tls")]
     NativeTls(TlsStream<TcpStream>),
     /// Encrypted TCP stream
-    #[cfg(feature = "rustls-tls")]
-    RustlsTls(StreamOwned<ClientConnection, TcpStream>),
+    #[cfg(feature = "rustls")]
+    Rustls(StreamOwned<ClientConnection, TcpStream>),
     #[cfg(feature = "boring-tls")]
     BoringTls(SslStream<TcpStream>),
     /// Can't be built
@@ -55,14 +55,14 @@ impl NetworkStream {
 
     /// 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(),
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref s) => s.get_ref().peer_addr(),
+            InnerNetworkStream::NativeTls(s) => s.get_ref().peer_addr(),
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(s) => s.get_ref().peer_addr(),
             #[cfg(feature = "boring-tls")]
-            InnerNetworkStream::BoringTls(ref s) => s.get_ref().peer_addr(),
+            InnerNetworkStream::BoringTls(s) => s.get_ref().peer_addr(),
             InnerNetworkStream::None => {
                 debug_assert!(false, "InnerNetworkStream::None must never be built");
                 Ok(SocketAddr::V4(SocketAddrV4::new(
@@ -75,14 +75,14 @@ impl NetworkStream {
 
     /// Shutdowns the connection
     pub fn shutdown(&self, how: Shutdown) -> io::Result<()> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref s) => s.shutdown(how),
+        match &self.inner {
+            InnerNetworkStream::Tcp(s) => s.shutdown(how),
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref s) => s.get_ref().shutdown(how),
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref s) => s.get_ref().shutdown(how),
+            InnerNetworkStream::NativeTls(s) => s.get_ref().shutdown(how),
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(s) => s.get_ref().shutdown(how),
             #[cfg(feature = "boring-tls")]
-            InnerNetworkStream::BoringTls(ref s) => s.get_ref().shutdown(how),
+            InnerNetworkStream::BoringTls(s) => s.get_ref().shutdown(how),
             InnerNetworkStream::None => {
                 debug_assert!(false, "InnerNetworkStream::None must never be built");
                 Ok(())
@@ -119,12 +119,12 @@ impl NetworkStream {
 
                 if let Some(timeout) = timeout {
                     match socket.connect_timeout(&addr.into(), timeout) {
-                        Ok(_) => return Ok(socket.into()),
+                        Ok(()) => return Ok(socket.into()),
                         Err(err) => last_err = Some(err),
                     }
                 } else {
                     match socket.connect(&addr.into()) {
-                        Ok(_) => return Ok(socket.into()),
+                        Ok(()) => return Ok(socket.into()),
                         Err(err) => last_err = Some(err),
                     }
                 }
@@ -146,23 +146,18 @@ impl NetworkStream {
 
     pub fn upgrade_tls(&mut self, tls_parameters: &TlsParameters) -> Result<(), Error> {
         match &self.inner {
-            #[cfg(not(any(
-                feature = "native-tls",
-                feature = "rustls-tls",
-                feature = "boring-tls"
-            )))]
+            #[cfg(not(any(feature = "native-tls", feature = "rustls", 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");
+                panic!("Trying to upgrade an NetworkStream without having enabled either the `native-tls` or the `rustls` feature");
             }
 
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-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!(),
+                let InnerNetworkStream::Tcp(tcp_stream) = tcp_stream else {
+                    unreachable!()
                 };
 
                 self.inner = Self::upgrade_tls_impl(tcp_stream, tls_parameters)?;
@@ -172,34 +167,37 @@ impl NetworkStream {
         }
     }
 
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
     fn upgrade_tls_impl(
         tcp_stream: TcpStream,
         tls_parameters: &TlsParameters,
     ) -> Result<InnerNetworkStream, Error> {
         Ok(match &tls_parameters.connector {
             #[cfg(feature = "native-tls")]
-            InnerTlsParameters::NativeTls(connector) => {
+            InnerTlsParameters::NativeTls { connector } => {
                 let stream = connector
                     .connect(tls_parameters.domain(), tcp_stream)
                     .map_err(error::connection)?;
                 InnerNetworkStream::NativeTls(stream)
             }
-            #[cfg(feature = "rustls-tls")]
-            InnerTlsParameters::RustlsTls(connector) => {
+            #[cfg(feature = "rustls")]
+            InnerTlsParameters::Rustls { config } => {
                 let domain = ServerName::try_from(tls_parameters.domain())
                     .map_err(|_| error::connection("domain isn't a valid DNS name"))?;
-                let connection = ClientConnection::new(Arc::clone(connector), domain)
+                let connection = ClientConnection::new(Arc::clone(config), domain.to_owned())
                     .map_err(error::connection)?;
                 let stream = StreamOwned::new(connection, tcp_stream);
-                InnerNetworkStream::RustlsTls(stream)
+                InnerNetworkStream::Rustls(stream)
             }
             #[cfg(feature = "boring-tls")]
-            InnerTlsParameters::BoringTls(connector) => {
+            InnerTlsParameters::BoringTls {
+                connector,
+                accept_invalid_hostnames,
+            } => {
                 let stream = connector
                     .configure()
                     .map_err(error::connection)?
-                    .verify_hostname(tls_parameters.accept_invalid_hostnames)
+                    .verify_hostname(*accept_invalid_hostnames)
                     .connect(tls_parameters.domain(), tcp_stream)
                     .map_err(error::connection)?;
                 InnerNetworkStream::BoringTls(stream)
@@ -208,12 +206,12 @@ impl NetworkStream {
     }
 
     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,
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(_) => true,
             #[cfg(feature = "boring-tls")]
             InnerNetworkStream::BoringTls(_) => true,
             InnerNetworkStream::None => {
@@ -223,7 +221,55 @@ impl NetworkStream {
         }
     }
 
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg(feature = "boring-tls")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "boring-tls")))]
+    pub fn tls_verify_result(&self) -> Result<(), Error> {
+        match &self.inner {
+            InnerNetworkStream::Tcp(_) => Err(error::client("Connection is not encrypted")),
+            #[cfg(feature = "native-tls")]
+            InnerNetworkStream::NativeTls(_) => panic!("Unsupported"),
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(_) => panic!("Unsupported"),
+            #[cfg(feature = "boring-tls")]
+            InnerNetworkStream::BoringTls(stream) => {
+                stream.ssl().verify_result().map_err(error::tls)
+            }
+            InnerNetworkStream::None => panic!("InnerNetworkStream::None must never be built"),
+        }
+    }
+
+    #[cfg(any(feature = "rustls", feature = "boring-tls"))]
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "rustls", feature = "boring-tls"))))]
+    pub fn certificate_chain(&self) -> Result<Vec<Vec<u8>>, Error> {
+        match &self.inner {
+            InnerNetworkStream::Tcp(_) => Err(error::client("Connection is not encrypted")),
+            #[cfg(feature = "native-tls")]
+            InnerNetworkStream::NativeTls(_) => panic!("Unsupported"),
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(stream) => Ok(stream
+                .conn
+                .peer_certificates()
+                .unwrap()
+                .iter()
+                .map(|c| c.to_vec())
+                .collect()),
+            #[cfg(feature = "boring-tls")]
+            InnerNetworkStream::BoringTls(stream) => Ok(stream
+                .ssl()
+                .peer_cert_chain()
+                .unwrap()
+                .iter()
+                .map(|c| c.to_der().map_err(error::tls))
+                .collect::<Result<Vec<_>, _>>()?),
+            InnerNetworkStream::None => panic!("InnerNetworkStream::None must never be built"),
+        }
+    }
+
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
+    )]
     pub fn peer_certificate(&self) -> Result<Vec<u8>, Error> {
         match &self.inner {
             InnerNetworkStream::Tcp(_) => Err(error::client("Connection is not encrypted")),
@@ -234,15 +280,14 @@ impl NetworkStream {
                 .unwrap()
                 .to_der()
                 .map_err(error::tls)?),
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(stream) => Ok(stream
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(stream) => Ok(stream
                 .conn
                 .peer_certificates()
                 .unwrap()
                 .first()
                 .unwrap()
-                .clone()
-                .0),
+                .to_vec()),
             #[cfg(feature = "boring-tls")]
             InnerNetworkStream::BoringTls(stream) => Ok(stream
                 .ssl()
@@ -255,20 +300,14 @@ impl NetworkStream {
     }
 
     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)
-            }
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut stream) => {
-                stream.get_ref().set_read_timeout(duration)
-            }
+            InnerNetworkStream::NativeTls(stream) => stream.get_ref().set_read_timeout(duration),
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(stream) => stream.get_ref().set_read_timeout(duration),
             #[cfg(feature = "boring-tls")]
-            InnerNetworkStream::BoringTls(ref mut stream) => {
-                stream.get_ref().set_read_timeout(duration)
-            }
+            InnerNetworkStream::BoringTls(stream) => stream.get_ref().set_read_timeout(duration),
             InnerNetworkStream::None => {
                 debug_assert!(false, "InnerNetworkStream::None must never be built");
                 Ok(())
@@ -278,21 +317,15 @@ impl NetworkStream {
 
     /// 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)
-            }
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut stream) => {
-                stream.get_ref().set_write_timeout(duration)
-            }
+            InnerNetworkStream::NativeTls(stream) => stream.get_ref().set_write_timeout(duration),
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(stream) => stream.get_ref().set_write_timeout(duration),
             #[cfg(feature = "boring-tls")]
-            InnerNetworkStream::BoringTls(ref mut stream) => {
-                stream.get_ref().set_write_timeout(duration)
-            }
+            InnerNetworkStream::BoringTls(stream) => stream.get_ref().set_write_timeout(duration),
             InnerNetworkStream::None => {
                 debug_assert!(false, "InnerNetworkStream::None must never be built");
                 Ok(())
@@ -303,14 +336,14 @@ impl NetworkStream {
 
 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),
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut s) => s.read(buf),
+            InnerNetworkStream::NativeTls(s) => s.read(buf),
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(s) => s.read(buf),
             #[cfg(feature = "boring-tls")]
-            InnerNetworkStream::BoringTls(ref mut s) => s.read(buf),
+            InnerNetworkStream::BoringTls(s) => s.read(buf),
             InnerNetworkStream::None => {
                 debug_assert!(false, "InnerNetworkStream::None must never be built");
                 Ok(0)
@@ -321,14 +354,14 @@ impl Read for NetworkStream {
 
 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),
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut s) => s.write(buf),
+            InnerNetworkStream::NativeTls(s) => s.write(buf),
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(s) => s.write(buf),
             #[cfg(feature = "boring-tls")]
-            InnerNetworkStream::BoringTls(ref mut s) => s.write(buf),
+            InnerNetworkStream::BoringTls(s) => s.write(buf),
             InnerNetworkStream::None => {
                 debug_assert!(false, "InnerNetworkStream::None must never be built");
                 Ok(0)
@@ -337,14 +370,14 @@ impl Write for NetworkStream {
     }
 
     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(),
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut s) => s.flush(),
+            InnerNetworkStream::NativeTls(s) => s.flush(),
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(s) => s.flush(),
             #[cfg(feature = "boring-tls")]
-            InnerNetworkStream::BoringTls(ref mut s) => s.flush(),
+            InnerNetworkStream::BoringTls(s) => s.flush(),
             InnerNetworkStream::None => {
                 debug_assert!(false, "InnerNetworkStream::None must never be built");
                 Ok(())
@@ -354,9 +387,9 @@ impl Write for NetworkStream {
 }
 
 /// 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 to the default
+/// 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
+/// See: <https://github.com/hyperium/hyper/blob/faf24c6ad8eee1c3d5ccc9a4d4835717b8e2903f/src/client/connect/http.rs#L560>
 fn bind_local_address(
     socket: &socket2::Socket,
     dst_addr: &SocketAddr,

src/transport/smtp/client/tls.rs

@@ -1,24 +1,31 @@
 use std::fmt::{self, Debug};
-#[cfg(feature = "rustls-tls")]
-use std::{sync::Arc, time::SystemTime};
+#[cfg(feature = "rustls")]
+use std::sync::Arc;
 
 #[cfg(feature = "boring-tls")]
-use boring::ssl::{SslConnector, SslVersion};
+use boring::{
+    pkey::PKey,
+    ssl::{SslConnector, SslVersion},
+    x509::store::X509StoreBuilder,
+};
 #[cfg(feature = "native-tls")]
 use native_tls::{Protocol, TlsConnector};
-#[cfg(feature = "rustls-tls")]
+#[cfg(feature = "rustls")]
 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, CryptoProvider},
+    pki_types::{self, pem::PemObject, CertificateDer, PrivateKeyDer, ServerName, UnixTime},
+    server::ParsedCertificate,
+    ClientConfig, DigitallySignedStruct, Error as TlsError, RootCertStore, SignatureScheme,
 };
 
-#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
 use crate::transport::smtp::{error, Error};
 
 /// TLS protocol versions.
 #[derive(Debug, Copy, Clone)]
 #[non_exhaustive]
-#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
 pub enum TlsVersion {
     /// TLS 1.0
     ///
@@ -44,38 +51,82 @@ pub enum TlsVersion {
     Tlsv12,
     /// TLS 1.3
     ///
-    /// The most secure option, altough not supported by all SMTP servers.
+    /// The most secure option, although not supported by all SMTP servers.
     ///
-    /// Altough it is technically supported by all TLS backends,
+    /// 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
+/// Specifies how to establish a TLS connection
+///
+/// TLDR: Use [`Tls::Wrapper`] or [`Tls::Required`] when
+/// connecting to a remote server, [`Tls::None`] when
+/// connecting to a local server.
 #[derive(Clone)]
 #[allow(missing_copy_implementations)]
+#[cfg_attr(
+    not(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")),
+    deprecated(
+        note = "starting from lettre v0.12 `Tls` won't be available when none of the TLS backends are enabled"
+    )
+)]
+#[cfg_attr(
+    docsrs,
+    doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
+)]
 pub enum Tls {
-    /// Insecure connection only (for testing purposes)
+    /// Insecure (plaintext) connection only.
+    ///
+    /// This option **always** uses a plaintext connection and should only
+    /// be used for trusted local relays. It is **highly discouraged**
+    /// for remote servers, as it exposes credentials and emails to potential
+    /// interception.
+    ///
+    /// Note: Servers requiring credentials or emails to be sent over TLS
+    /// may reject connections when this option is used.
     None,
-    /// Start with insecure connection and use `STARTTLS` when available
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    /// Begin with a plaintext connection and attempt to use `STARTTLS` if available.
+    ///
+    /// lettre will try to upgrade to a TLS-secured connection but will fall back
+    /// to plaintext if the server does not support TLS. This option is provided for
+    /// compatibility but is **strongly discouraged**, as it exposes connections to
+    /// potential MITM (man-in-the-middle) attacks.
+    ///
+    /// Warning: A malicious intermediary could intercept the `STARTTLS` flag,
+    /// causing lettre to believe the server only supports plaintext connections.
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
     #[cfg_attr(
         docsrs,
-        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
     )]
     Opportunistic(TlsParameters),
-    /// Start with insecure connection and require `STARTTLS`
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    /// Begin with a plaintext connection and require `STARTTLS` for security.
+    ///
+    /// lettre will upgrade plaintext TCP connections to TLS before transmitting
+    /// any sensitive data. If the server does not support TLS, the connection
+    /// attempt will fail, ensuring no credentials or emails are sent in plaintext.
+    ///
+    /// Unlike [`Tls::Opportunistic`], this option is secure against MITM attacks.
+    /// For optimal security and performance, consider using [`Tls::Wrapper`] instead,
+    /// as it requires fewer roundtrips to establish a secure connection.
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
     #[cfg_attr(
         docsrs,
-        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
     )]
     Required(TlsParameters),
-    /// Use TLS wrapped connection
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    /// Establish a connection wrapped in TLS from the start.
+    ///
+    /// lettre connects to the server and immediately performs a TLS handshake.
+    /// If the handshake fails, the connection attempt is aborted without
+    /// transmitting any sensitive data.
+    ///
+    /// This is the fastest and most secure option for establishing a connection.
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
     #[cfg_attr(
         docsrs,
-        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
     )]
     Wrapper(TlsParameters),
 }
@@ -84,34 +135,89 @@ 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", feature = "boring-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
             Self::Opportunistic(_) => f.pad("Opportunistic"),
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
             Self::Required(_) => f.pad("Required"),
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls", 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)]
+#[cfg_attr(
+    not(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")),
+    deprecated(
+        note = "starting from lettre v0.12 `CertificateStore` won't be available when none of the TLS backends are enabled"
+    )
+)]
+#[cfg_attr(
+    docsrs,
+    doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
+)]
+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 use the system certificate verifier if the `rustls-platform-verifier`
+    /// feature is enabled. If the `rustls-native-certs` feature is enabled, system certificate
+    /// store will be used. Otherwise, it 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(all(feature = "rustls", feature = "webpki-roots"))]
+    WebpkiRoots,
+    /// Don't use any system certificates.
+    None,
+}
+
 /// Parameters to use for secure clients
 #[derive(Clone)]
+#[cfg_attr(
+    not(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")),
+    deprecated(
+        note = "starting from lettre v0.12 `TlsParameters` won't be available when none of the TLS backends are enabled"
+    )
+)]
+#[cfg_attr(
+    docsrs,
+    doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
+)]
 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)]
+#[cfg_attr(
+    not(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")),
+    deprecated(
+        note = "starting from lettre v0.12 `TlsParametersBuilder` won't be available when none of the TLS backends are enabled"
+    )
+)]
+#[cfg_attr(
+    docsrs,
+    doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
+)]
 pub struct TlsParametersBuilder {
     domain: String,
+    cert_store: CertificateStore,
     root_certs: Vec<Certificate>,
+    identity: Option<Identity>,
     accept_invalid_hostnames: bool,
     accept_invalid_certs: bool,
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
     min_tls_version: TlsVersion,
 }
 
@@ -120,24 +226,42 @@ impl TlsParametersBuilder {
     pub fn new(domain: String) -> Self {
         Self {
             domain,
+            cert_store: CertificateStore::Default,
             root_certs: Vec::new(),
+            identity: None,
             accept_invalid_hostnames: false,
             accept_invalid_certs: false,
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls", 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.
+    /// Can be used to safely connect to a server using a self-signed certificate, for example.
     pub fn add_root_certificate(mut self, cert: Certificate) -> Self {
         self.root_certs.push(cert);
         self
     }
 
+    /// Add a client certificate
+    ///
+    /// Can be used to configure a client certificate to present to the server.
+    pub fn identify_with(mut self, identity: Identity) -> Self {
+        self.identity = Some(identity);
+        self
+    }
+
     /// Controls whether certificates with an invalid hostname are accepted
     ///
+    /// This option is silently disabled when using `rustls-platform-verifier`.
+    ///
     /// Defaults to `false`.
     ///
     /// # Warning
@@ -147,10 +271,11 @@ impl TlsParametersBuilder {
     /// including those from other sites, are trusted.
     ///
     /// This method introduces significant vulnerabilities to man-in-the-middle attacks.
-    ///
-    /// Hostname verification can only be disabled with the `native-tls` TLS backend.
-    #[cfg(any(feature = "native-tls", feature = "boring-tls"))]
-    #[cfg_attr(docsrs, doc(cfg(any(feature = "native-tls", feature = "boring-tls"))))]
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
+    )]
     pub fn dangerous_accept_invalid_hostnames(mut self, accept_invalid_hostnames: bool) -> Self {
         self.accept_invalid_hostnames = accept_invalid_hostnames;
         self
@@ -159,7 +284,11 @@ impl TlsParametersBuilder {
     /// Controls which minimum TLS version is allowed
     ///
     /// Defaults to [`Tlsv12`][TlsVersion::Tlsv12].
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
+    )]
     pub fn set_min_tls_version(mut self, min_tls_version: TlsVersion) -> Self {
         self.min_tls_version = min_tls_version;
         self
@@ -188,17 +317,17 @@ impl TlsParametersBuilder {
 
     /// 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", feature = "boring-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
     #[cfg_attr(
         docsrs,
-        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
     )]
     pub fn build(self) -> Result<TlsParameters, Error> {
-        #[cfg(feature = "rustls-tls")]
+        #[cfg(feature = "rustls")]
         return self.build_rustls();
-        #[cfg(all(not(feature = "rustls-tls"), feature = "native-tls"))]
+        #[cfg(all(not(feature = "rustls"), feature = "native-tls"))]
         return self.build_native();
-        #[cfg(all(not(feature = "rustls-tls"), feature = "boring-tls"))]
+        #[cfg(all(not(feature = "rustls"), feature = "boring-tls"))]
         return self.build_boring();
     }
 
@@ -208,6 +337,18 @@ 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);
         }
@@ -226,12 +367,14 @@ impl TlsParametersBuilder {
         };
 
         tls_builder.min_protocol_version(Some(min_tls_version));
+        if let Some(identity) = self.identity {
+            tls_builder.identity(identity.native_tls);
+        }
+
         let connector = tls_builder.build().map_err(error::tls)?;
         Ok(TlsParameters {
-            connector: InnerTlsParameters::NativeTls(connector),
+            connector: InnerTlsParameters::NativeTls { connector },
             domain: self.domain,
-            #[cfg(feature = "boring-tls")]
-            accept_invalid_hostnames: self.accept_invalid_hostnames,
         })
     }
 
@@ -246,6 +389,21 @@ impl TlsParametersBuilder {
         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 {
@@ -253,6 +411,15 @@ impl TlsParametersBuilder {
             }
         }
 
+        if let Some(identity) = self.identity {
+            tls_builder
+                .set_certificate(identity.boring_tls.0.as_ref())
+                .map_err(error::tls)?;
+            tls_builder
+                .set_private_key(identity.boring_tls.1.as_ref())
+                .map_err(error::tls)?;
+        }
+
         let min_tls_version = match self.min_tls_version {
             TlsVersion::Tlsv10 => SslVersion::TLS1,
             TlsVersion::Tlsv11 => SslVersion::TLS1_1,
@@ -265,18 +432,18 @@ impl TlsParametersBuilder {
             .map_err(error::tls)?;
         let connector = tls_builder.build();
         Ok(TlsParameters {
-            connector: InnerTlsParameters::BoringTls(connector),
+            connector: InnerTlsParameters::BoringTls {
+                connector,
+                accept_invalid_hostnames: self.accept_invalid_hostnames,
+            },
             domain: self.domain,
-            accept_invalid_hostnames: self.accept_invalid_hostnames,
         })
     }
 
     /// Creates a new `TlsParameters` using rustls with the provided configuration
-    #[cfg(feature = "rustls-tls")]
-    #[cfg_attr(docsrs, doc(cfg(feature = "rustls-tls")))]
+    #[cfg(feature = "rustls")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "rustls")))]
     pub fn build_rustls(self) -> Result<TlsParameters, Error> {
-        let tls = ClientConfig::builder();
-
         let just_version3 = &[&rustls::version::TLS13];
         let supported_versions = match self.min_tls_version {
             TlsVersion::Tlsv10 => {
@@ -289,65 +456,144 @@ impl TlsParametersBuilder {
             TlsVersion::Tlsv13 => just_version3,
         };
 
-        let tls = tls
-            .with_safe_default_cipher_suites()
-            .with_safe_default_kx_groups()
+        let crypto_provider = crate::rustls_crypto::crypto_provider();
+        let tls = ClientConfig::builder_with_provider(Arc::clone(&crypto_provider))
             .with_protocol_versions(supported_versions)
             .map_err(error::tls)?;
 
-        let tls = if self.accept_invalid_certs {
-            tls.with_custom_certificate_verifier(Arc::new(InvalidCertsVerifier {}))
-        } else {
-            let mut root_cert_store = RootCertStore::empty();
-            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_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,
-                    )
-                },
-            ));
+        // Build TLS config
+        let mut root_cert_store = RootCertStore::empty();
 
-            tls.with_custom_certificate_verifier(Arc::new(WebPkiVerifier::new(
-                root_cert_store,
-                None,
-            )))
+        #[cfg(all(
+            not(feature = "rustls-platform-verifier"),
+            feature = "rustls-native-certs"
+        ))]
+        fn load_native_roots(store: &mut RootCertStore) {
+            let rustls_native_certs::CertificateResult { certs, errors, .. } =
+                rustls_native_certs::load_native_certs();
+            let errors_len = errors.len();
+
+            let (added, ignored) = store.add_parsable_certificates(certs);
+            #[cfg(feature = "tracing")]
+            tracing::debug!(
+                "loaded platform certs with {errors_len} failing to load, {added} valid and {ignored} ignored (invalid) certs"
+            );
+            #[cfg(not(feature = "tracing"))]
+            let _ = (errors_len, added, ignored);
+        }
+
+        #[cfg(all(feature = "rustls", feature = "webpki-roots"))]
+        fn load_webpki_roots(store: &mut RootCertStore) {
+            store.extend(webpki_roots::TLS_SERVER_ROOTS.iter().cloned());
+        }
+
+        #[cfg_attr(not(feature = "rustls-platform-verifier"), allow(unused_mut))]
+        let mut extra_roots = None::<Vec<CertificateDer<'static>>>;
+        match self.cert_store {
+            CertificateStore::Default => {
+                #[cfg(feature = "rustls-platform-verifier")]
+                {
+                    extra_roots = Some(Vec::new());
+                }
+
+                #[cfg(all(
+                    not(feature = "rustls-platform-verifier"),
+                    feature = "rustls-native-certs"
+                ))]
+                load_native_roots(&mut root_cert_store);
+
+                #[cfg(all(
+                    not(feature = "rustls-platform-verifier"),
+                    not(feature = "rustls-native-certs"),
+                    feature = "webpki-roots"
+                ))]
+                load_webpki_roots(&mut root_cert_store);
+            }
+            #[cfg(all(feature = "rustls", feature = "webpki-roots"))]
+            CertificateStore::WebpkiRoots => {
+                load_webpki_roots(&mut root_cert_store);
+            }
+            CertificateStore::None => {}
+        }
+        for cert in self.root_certs {
+            for rustls_cert in cert.rustls {
+                #[cfg(feature = "rustls-platform-verifier")]
+                if let Some(extra_roots) = &mut extra_roots {
+                    extra_roots.push(rustls_cert.clone());
+                }
+                root_cert_store.add(rustls_cert).map_err(error::tls)?;
+            }
+        }
+
+        let tls = if self.accept_invalid_certs
+            || (extra_roots.is_none() && self.accept_invalid_hostnames)
+        {
+            let verifier = InvalidCertsVerifier {
+                ignore_invalid_hostnames: self.accept_invalid_hostnames,
+                ignore_invalid_certs: self.accept_invalid_certs,
+                roots: root_cert_store,
+                crypto_provider,
+            };
+            tls.dangerous()
+                .with_custom_certificate_verifier(Arc::new(verifier))
+        } else {
+            #[cfg(feature = "rustls-platform-verifier")]
+            if let Some(extra_roots) = extra_roots {
+                tls.dangerous().with_custom_certificate_verifier(Arc::new(
+                    rustls_platform_verifier::Verifier::new_with_extra_roots(
+                        extra_roots,
+                        crypto_provider,
+                    )
+                    .map_err(error::tls)?,
+                ))
+            } else {
+                tls.with_root_certificates(root_cert_store)
+            }
+
+            #[cfg(not(feature = "rustls-platform-verifier"))]
+            {
+                tls.with_root_certificates(root_cert_store)
+            }
+        };
+
+        let tls = if let Some(identity) = self.identity {
+            let (client_certificates, private_key) = identity.rustls_tls;
+            tls.with_client_auth_cert(client_certificates, private_key)
+                .map_err(error::tls)?
+        } else {
+            tls.with_no_client_auth()
         };
-        let tls = tls.with_no_client_auth();
 
         Ok(TlsParameters {
-            connector: InnerTlsParameters::RustlsTls(Arc::new(tls)),
+            connector: InnerTlsParameters::Rustls {
+                config: 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 {
+pub(crate) enum InnerTlsParameters {
     #[cfg(feature = "native-tls")]
-    NativeTls(TlsConnector),
-    #[cfg(feature = "rustls-tls")]
-    RustlsTls(Arc<ClientConfig>),
+    NativeTls { connector: TlsConnector },
+    #[cfg(feature = "rustls")]
+    Rustls { config: Arc<ClientConfig> },
     #[cfg(feature = "boring-tls")]
-    BoringTls(SslConnector),
+    BoringTls {
+        connector: SslConnector,
+        accept_invalid_hostnames: bool,
+    },
 }
 
 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", feature = "boring-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
     #[cfg_attr(
         docsrs,
-        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
     )]
     pub fn new(domain: String) -> Result<Self, Error> {
         TlsParametersBuilder::new(domain).build()
@@ -366,8 +612,8 @@ impl TlsParameters {
     }
 
     /// Creates a new `TlsParameters` using rustls
-    #[cfg(feature = "rustls-tls")]
-    #[cfg_attr(docsrs, doc(cfg(feature = "rustls-tls")))]
+    #[cfg(feature = "rustls")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "rustls")))]
     pub fn new_rustls(domain: String) -> Result<Self, Error> {
         TlsParametersBuilder::new(domain).build_rustls()
     }
@@ -384,19 +630,29 @@ impl TlsParameters {
     }
 }
 
-/// A client certificate that can be used with [`TlsParametersBuilder::add_root_certificate`]
+/// A certificate that can be used with [`TlsParametersBuilder::add_root_certificate`]
 #[derive(Clone)]
 #[allow(missing_copy_implementations)]
+#[cfg_attr(
+    not(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")),
+    deprecated(
+        note = "starting from lettre v0.12 `Certificate` won't be available when none of the TLS backends are enabled"
+    )
+)]
+#[cfg_attr(
+    docsrs,
+    doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
+)]
 pub struct Certificate {
     #[cfg(feature = "native-tls")]
     native_tls: native_tls::Certificate,
-    #[cfg(feature = "rustls-tls")]
-    rustls: Vec<rustls::Certificate>,
+    #[cfg(feature = "rustls")]
+    rustls: Vec<CertificateDer<'static>>,
     #[cfg(feature = "boring-tls")]
     boring_tls: boring::x509::X509,
 }
 
-#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
 impl Certificate {
     /// Create a `Certificate` from a DER encoded certificate
     pub fn from_der(der: Vec<u8>) -> Result<Self, Error> {
@@ -409,8 +665,8 @@ impl Certificate {
         Ok(Self {
             #[cfg(feature = "native-tls")]
             native_tls: native_tls_cert,
-            #[cfg(feature = "rustls-tls")]
-            rustls: vec![rustls::Certificate(der)],
+            #[cfg(feature = "rustls")]
+            rustls: vec![der.into()],
             #[cfg(feature = "boring-tls")]
             boring_tls: boring_tls_cert,
         })
@@ -424,22 +680,17 @@ impl Certificate {
         #[cfg(feature = "boring-tls")]
         let boring_tls_cert = boring::x509::X509::from_pem(pem).map_err(error::tls)?;
 
-        #[cfg(feature = "rustls-tls")]
+        #[cfg(feature = "rustls")]
         let rustls_cert = {
-            use std::io::Cursor;
-
-            let mut pem = Cursor::new(pem);
-            rustls_pemfile::certs(&mut pem)
+            CertificateDer::pem_slice_iter(pem)
+                .collect::<Result<Vec<_>, pki_types::pem::Error>>()
                 .map_err(|_| error::tls("invalid certificates"))?
-                .into_iter()
-                .map(rustls::Certificate)
-                .collect::<Vec<_>>()
         };
 
         Ok(Self {
             #[cfg(feature = "native-tls")]
             native_tls: native_tls_cert,
-            #[cfg(feature = "rustls-tls")]
+            #[cfg(feature = "rustls")]
             rustls: rustls_cert,
             #[cfg(feature = "boring-tls")]
             boring_tls: boring_tls_cert,
@@ -453,20 +704,159 @@ impl Debug for Certificate {
     }
 }
 
-#[cfg(feature = "rustls-tls")]
-struct InvalidCertsVerifier;
+/// An identity that can be used with [`TlsParametersBuilder::identify_with`]
+#[allow(missing_copy_implementations)]
+#[cfg_attr(
+    not(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")),
+    deprecated(
+        note = "starting from lettre v0.12 `Identity` won't be available when none of the TLS backends are enabled"
+    )
+)]
+#[cfg_attr(
+    docsrs,
+    doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
+)]
+pub struct Identity {
+    #[cfg(feature = "native-tls")]
+    native_tls: native_tls::Identity,
+    #[cfg(feature = "rustls")]
+    rustls_tls: (Vec<CertificateDer<'static>>, PrivateKeyDer<'static>),
+    #[cfg(feature = "boring-tls")]
+    boring_tls: (boring::x509::X509, PKey<boring::pkey::Private>),
+}
 
-#[cfg(feature = "rustls-tls")]
+impl Debug for Identity {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Identity").finish()
+    }
+}
+
+impl Clone for Identity {
+    fn clone(&self) -> Self {
+        Identity {
+            #[cfg(feature = "native-tls")]
+            native_tls: self.native_tls.clone(),
+            #[cfg(feature = "rustls")]
+            rustls_tls: (self.rustls_tls.0.clone(), self.rustls_tls.1.clone_key()),
+            #[cfg(feature = "boring-tls")]
+            boring_tls: (self.boring_tls.0.clone(), self.boring_tls.1.clone()),
+        }
+    }
+}
+
+#[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
+impl Identity {
+    pub fn from_pem(pem: &[u8], key: &[u8]) -> Result<Self, Error> {
+        Ok(Self {
+            #[cfg(feature = "native-tls")]
+            native_tls: Identity::from_pem_native_tls(pem, key)?,
+            #[cfg(feature = "rustls")]
+            rustls_tls: Identity::from_pem_rustls_tls(pem, key)?,
+            #[cfg(feature = "boring-tls")]
+            boring_tls: Identity::from_pem_boring_tls(pem, key)?,
+        })
+    }
+
+    #[cfg(feature = "native-tls")]
+    fn from_pem_native_tls(pem: &[u8], key: &[u8]) -> Result<native_tls::Identity, Error> {
+        native_tls::Identity::from_pkcs8(pem, key).map_err(error::tls)
+    }
+
+    #[cfg(feature = "rustls")]
+    fn from_pem_rustls_tls(
+        pem: &[u8],
+        key: &[u8],
+    ) -> Result<(Vec<CertificateDer<'static>>, PrivateKeyDer<'static>), Error> {
+        let key = match PrivateKeyDer::from_pem_slice(key) {
+            Ok(key) => key,
+            Err(pki_types::pem::Error::NoItemsFound) => {
+                return Err(error::tls("no private key found"))
+            }
+            Err(err) => return Err(error::tls(err)),
+        };
+
+        Ok((vec![pem.to_owned().into()], key))
+    }
+
+    #[cfg(feature = "boring-tls")]
+    fn from_pem_boring_tls(
+        pem: &[u8],
+        key: &[u8],
+    ) -> Result<(boring::x509::X509, PKey<boring::pkey::Private>), Error> {
+        let cert = boring::x509::X509::from_pem(pem).map_err(error::tls)?;
+        let key = boring::pkey::PKey::private_key_from_pem(key).map_err(error::tls)?;
+        Ok((cert, key))
+    }
+}
+
+#[cfg(feature = "rustls")]
+#[derive(Debug)]
+struct InvalidCertsVerifier {
+    ignore_invalid_hostnames: bool,
+    ignore_invalid_certs: bool,
+    roots: RootCertStore,
+    crypto_provider: Arc<CryptoProvider>,
+}
+
+#[cfg(feature = "rustls")]
 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> {
+        let cert = ParsedCertificate::try_from(end_entity)?;
+
+        if !self.ignore_invalid_certs {
+            rustls::client::verify_server_cert_signed_by_trust_anchor(
+                &cert,
+                &self.roots,
+                intermediates,
+                now,
+                self.crypto_provider.signature_verification_algorithms.all,
+            )?;
+        }
+
+        if !self.ignore_invalid_hostnames {
+            rustls::client::verify_server_name(&cert, server_name)?;
+        }
         Ok(ServerCertVerified::assertion())
     }
+
+    fn verify_tls12_signature(
+        &self,
+        message: &[u8],
+        cert: &CertificateDer<'_>,
+        dss: &DigitallySignedStruct,
+    ) -> Result<HandshakeSignatureValid, TlsError> {
+        verify_tls12_signature(
+            message,
+            cert,
+            dss,
+            &self.crypto_provider.signature_verification_algorithms,
+        )
+    }
+
+    fn verify_tls13_signature(
+        &self,
+        message: &[u8],
+        cert: &CertificateDer<'_>,
+        dss: &DigitallySignedStruct,
+    ) -> Result<HandshakeSignatureValid, TlsError> {
+        verify_tls13_signature(
+            message,
+            cert,
+            dss,
+            &self.crypto_provider.signature_verification_algorithms,
+        )
+    }
+
+    fn supported_verify_schemes(&self) -> Vec<SignatureScheme> {
+        self.crypto_provider
+            .signature_verification_algorithms
+            .supported_schemes()
+    }
 }

src/transport/smtp/commands.rs

@@ -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!(
@@ -346,19 +346,13 @@ mod test {
         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!("{}", 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_string(), "password".to_string());
+        let credentials = Credentials::new("user".to_owned(), "password".to_owned());
         assert_eq!(
             format!(
                 "{}",

src/transport/smtp/connection_url.rs

@@ -0,0 +1,134 @@
+use std::borrow::Cow;
+
+use url::Url;
+
+#[cfg(any(feature = "native-tls", feature = "rustls", 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;
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
+    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)
+    }
+
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
+    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)
+    }
+
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
+    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", 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", 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", 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::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

@@ -68,15 +68,20 @@ impl Error {
     }
 
     /// Returns true if the error is from TLS
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
     #[cfg_attr(
         docsrs,
-        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
     )]
     pub fn is_tls(&self) -> bool {
         matches!(self.inner.kind, Kind::Tls)
     }
 
+    /// Returns true if the error is because the transport was shut down
+    pub fn is_transport_shutdown(&self) -> bool {
+        matches!(self.inner.kind, Kind::TransportShutdown)
+    }
+
     /// Returns the status code, if the error was generated from a response.
     pub fn status(&self) -> Option<Code> {
         match self.inner.kind {
@@ -107,10 +112,12 @@ pub(crate) enum Kind {
     /// TLS error
     #[cfg_attr(
         docsrs,
-        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
     )]
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
     Tls,
+    /// Transport shutdown error
+    TransportShutdown,
 }
 
 impl fmt::Debug for Error {
@@ -119,7 +126,7 @@ 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);
         }
 
@@ -129,22 +136,23 @@ 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", feature = "boring-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
             Kind::Tls => f.write_str("tls error")?,
-            Kind::Transient(ref code) => {
+            Kind::TransportShutdown => f.write_str("transport has been shut down")?,
+            Kind::Transient(code) => {
                 write!(f, "transient error ({code})")?;
             }
-            Kind::Permanent(ref code) => {
+            Kind::Permanent(code) => {
                 write!(f, "permanent error ({code})")?;
             }
-        };
+        }
 
-        if let Some(ref e) = self.inner.source {
+        if let Some(e) = &self.inner.source {
             write!(f, ": {e}")?;
         }
 
@@ -185,7 +193,11 @@ pub(crate) fn connection<E: Into<BoxError>>(e: E) -> Error {
     Error::new(Kind::Connection, Some(e))
 }
 
-#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
 pub(crate) fn tls<E: Into<BoxError>>(e: E) -> Error {
     Error::new(Kind::Tls, Some(e))
 }
+
+pub(crate) fn transport_shutdown() -> Error {
+    Error::new::<BoxError>(Kind::TransportShutdown, None)
+}

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)
         };
@@ -130,9 +129,8 @@ impl Display for ServerInfo {
 impl ServerInfo {
     /// Parses a EHLO response to create a `ServerInfo`
     pub fn from_response(response: &Response) -> Result<ServerInfo, Error> {
-        let name = match response.first_word() {
-            Some(name) => name,
-            None => return Err(error::response("Could not read server name")),
+        let Some(name) = response.first_word() else {
+            return Err(error::response("Could not read server name"));
         };
 
         let mut features: HashSet<Extension> = HashSet::new();
@@ -170,11 +168,11 @@ impl ServerInfo {
                     }
                 }
                 _ => (),
-            };
+            }
         }
 
         Ok(ServerInfo {
-            name: name.to_string(),
+            name: name.to_owned(),
             features,
         })
     }
@@ -190,7 +188,7 @@ 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 +225,16 @@ 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}"),
+        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 +275,13 @@ 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),
         }
@@ -292,33 +290,27 @@ impl Display for RcptParameter {
 
 #[cfg(test)]
 mod test {
-
-    use std::collections::HashSet;
-
     use super::*;
-    use crate::transport::smtp::{
-        authentication::Mechanism,
-        response::{Category, Code, Detail, Response, Severity},
-    };
+    use crate::transport::smtp::response::{Category, Code, Detail, Severity};
 
     #[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 +323,11 @@ 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 +336,11 @@ 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 +350,11 @@ 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 +366,14 @@ 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 +389,10 @@ 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 +402,7 @@ 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

@@ -26,43 +26,17 @@
 //!
 //! The relay server can be the local email server, a specific host or a third-party service.
 //!
-//! #### Simple example
+//! #### Simple example with authentication
 //!
-//! This is the most basic example of usage:
+//! A good starting point for sending emails via SMTP relay is to
+//! do the following:
 //!
 //! ```rust,no_run
-//! # #[cfg(all(feature = "builder", any(feature = "native-tls", feature = "rustls-tls")))]
-//! # fn test() -> Result<(), Box<dyn std::error::Error>> {
-//! use lettre::{Message, SmtpTransport, Transport};
-//!
-//! let email = Message::builder()
-//!     .from("NoBody <nobody@domain.tld>".parse()?)
-//!     .reply_to("Yuin <yuin@domain.tld>".parse()?)
-//!     .to("Hei <hei@domain.tld>".parse()?)
-//!     .subject("Happy new year")
-//!     .body(String::from("Be happy!"))?;
-//!
-//! // Create TLS transport on port 465
-//! let sender = SmtpTransport::relay("smtp.example.com")?.build();
-//! // Send the email via remote relay
-//! let result = sender.send(&email);
-//! assert!(result.is_ok());
-//! # Ok(())
-//! # }
-//! ```
-//!
-//! #### Authentication
-//!
-//! Example with authentication and connection pool:
-//!
-//! ```rust,no_run
-//! # #[cfg(all(feature = "builder", any(feature = "native-tls", feature = "rustls-tls")))]
+//! # #[cfg(all(feature = "builder", any(feature = "native-tls", feature = "rustls")))]
 //! # fn test() -> Result<(), Box<dyn std::error::Error>> {
 //! use lettre::{
-//!     transport::smtp::{
-//!         authentication::{Credentials, Mechanism},
-//!         PoolConfig,
-//!     },
+//!     message::header::ContentType,
+//!     transport::smtp::authentication::{Credentials, Mechanism},
 //!     Message, SmtpTransport, Transport,
 //! };
 //!
@@ -71,35 +45,39 @@
 //!     .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!"))?;
 //!
-//! // Create TLS transport on port 587 with STARTTLS
-//! let sender = SmtpTransport::starttls_relay("smtp.example.com")?
+//! // Create the SMTPS transport
+//! let sender = SmtpTransport::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
+//!     // Optionally configure expected authentication mechanism
 //!     .authentication(vec![Mechanism::Plain])
-//!     // Connection pool settings
-//!     .pool_config(PoolConfig::new().max_size(20))
 //!     .build();
 //!
 //! // Send the email via remote relay
-//! let result = sender.send(&email);
-//! assert!(result.is_ok());
+//! sender.send(&email)?;
 //! # Ok(())
 //! # }
 //! ```
 //!
-//! You can specify custom TLS settings:
+//! #### Shortening configuration
+//!
+//! It can be very repetitive to ask the user for every SMTP connection parameter.
+//! In some cases this can be simplified by using a connection URI instead.
+//!
+//! For more information take a look at [`SmtpTransport::from_url`] or [`AsyncSmtpTransport::from_url`].
 //!
 //! ```rust,no_run
-//! # #[cfg(all(feature = "builder", any(feature = "native-tls", feature = "rustls-tls")))]
+//! # #[cfg(all(feature = "builder", any(feature = "native-tls", feature = "rustls")))]
 //! # fn test() -> Result<(), Box<dyn std::error::Error>> {
 //! use lettre::{
-//!     transport::smtp::client::{Tls, TlsParameters},
+//!     message::header::ContentType,
+//!     transport::smtp::authentication::{Credentials, Mechanism},
 //!     Message, SmtpTransport, Transport,
 //! };
 //!
@@ -108,25 +86,106 @@
 //!     .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!"))?;
 //!
-//! // Custom TLS configuration
-//! let tls = TlsParameters::builder("smtp.example.com".to_string())
-//!     .dangerous_accept_invalid_certs(true)
+//! // Create the SMTPS transport
+//! let sender = SmtpTransport::from_url("smtps://username:password@smtp.example.com")?.build();
+//!
+//! // Send the email via remote relay
+//! sender.send(&email)?;
+//! # Ok(())
+//! # }
+//! ```
+//!
+//! #### Advanced configuration with custom TLS settings
+//!
+//! ```rust,no_run
+//! # #[cfg(all(feature = "builder", any(feature = "native-tls", feature = "rustls")))]
+//! # fn test() -> Result<(), Box<dyn std::error::Error>> {
+//! use std::fs;
+//!
+//! use lettre::{
+//!     message::header::ContentType,
+//!     transport::smtp::client::{Certificate, Tls, TlsParameters},
+//!     Message, SmtpTransport, Transport,
+//! };
+//!
+//! let email = Message::builder()
+//!     .from("NoBody <nobody@domain.tld>".parse()?)
+//!     .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!"))?;
+//!
+//! // Custom TLS configuration - Use a self signed certificate
+//! let cert = fs::read("self-signed.crt")?;
+//! let cert = Certificate::from_pem(&cert)?;
+//! let tls = TlsParameters::builder(/* TLS SNI value */ "smtp.example.com".to_owned())
+//!     .add_root_certificate(cert)
 //!     .build()?;
 //!
-//! // Create TLS transport on port 465
+//! // Create the SMTPS transport
 //! let sender = SmtpTransport::relay("smtp.example.com")?
-//!     // Custom TLS configuration
-//!     .tls(Tls::Required(tls))
+//!     .tls(Tls::Wrapper(tls))
 //!     .build();
 //!
 //! // Send the email via remote relay
-//! let result = sender.send(&email);
-//! assert!(result.is_ok());
+//! sender.send(&email)?;
 //! # Ok(())
 //! # }
 //! ```
+//!
+//! #### Connection pooling
+//!
+//! [`SmtpTransport`] and [`AsyncSmtpTransport`] store connections in
+//! a connection pool by default. This avoids connecting and disconnecting
+//! from the relay server for every message the application tries to send. For the connection pool
+//! to work the instance of the transport **must** be reused.
+//! In a webserver context it may go about this:
+//!
+//! ```rust,no_run
+//! # #[cfg(all(feature = "builder", any(feature = "native-tls", feature = "rustls")))]
+//! # fn test() {
+//! use lettre::{
+//!     message::header::ContentType,
+//!     transport::smtp::{authentication::Credentials, PoolConfig},
+//!     Message, SmtpTransport, Transport,
+//! };
+//! #
+//! # type Result<T> = std::result::Result<T, Box<dyn std::error::Error>>;
+//!
+//! /// The global application state
+//! #[derive(Debug)]
+//! struct AppState {
+//!     smtp: SmtpTransport,
+//!     // ... other global application parameters
+//! }
+//!
+//! impl AppState {
+//!     pub fn new(smtp_url: &str) -> Result<Self> {
+//!         let smtp = SmtpTransport::from_url(smtp_url)?.build();
+//!         Ok(Self { smtp })
+//!     }
+//! }
+//!
+//! fn handle_request(app_state: &AppState) -> Result<String> {
+//!     let email = Message::builder()
+//!         .from("NoBody <nobody@domain.tld>".parse()?)
+//!         .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!"))?;
+//!
+//!     // Send the email via remote relay
+//!     app_state.smtp.send(&email)?;
+//!
+//!     Ok("The email has successfully been sent!".to_owned())
+//! }
+//! # }
+//! ```
 
 use std::time::Duration;
 
@@ -140,7 +199,7 @@ pub use self::{
     error::Error,
     transport::{SmtpTransport, SmtpTransportBuilder},
 };
-#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
 use crate::transport::smtp::client::TlsParameters;
 use crate::transport::smtp::{
     authentication::{Credentials, Mechanism, DEFAULT_MECHANISMS},
@@ -154,6 +213,7 @@ 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 +260,7 @@ 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

@@ -1,8 +1,7 @@
 use std::{
     fmt::{self, Debug},
-    mem,
     ops::{Deref, DerefMut},
-    sync::Arc,
+    sync::{Arc, OnceLock},
     time::{Duration, Instant},
 };
 
@@ -10,19 +9,22 @@ use futures_util::{
     lock::Mutex,
     stream::{self, StreamExt},
 };
-use once_cell::sync::OnceCell;
 
 use super::{
     super::{client::AsyncSmtpConnection, Error},
     PoolConfig,
 };
-use crate::{executor::SpawnHandle, transport::smtp::async_transport::AsyncSmtpClient, Executor};
+use crate::{
+    executor::SpawnHandle,
+    transport::smtp::{async_transport::AsyncSmtpClient, error},
+    Executor,
+};
 
-pub struct Pool<E: Executor> {
+pub(crate) struct Pool<E: Executor> {
     config: PoolConfig,
-    connections: Mutex<Vec<ParkedConnection>>,
+    connections: Mutex<Option<Vec<ParkedConnection>>>,
     client: AsyncSmtpClient<E>,
-    handle: OnceCell<E::Handle>,
+    handle: OnceLock<E::Handle>,
 }
 
 struct ParkedConnection {
@@ -30,18 +32,18 @@ struct ParkedConnection {
     since: Instant,
 }
 
-pub struct PooledConnection<E: Executor> {
+pub(crate) struct PooledConnection<E: Executor> {
     conn: Option<AsyncSmtpConnection>,
     pool: Arc<Pool<E>>,
 }
 
 impl<E: Executor> Pool<E> {
-    pub fn new(config: PoolConfig, client: AsyncSmtpClient<E>) -> Arc<Self> {
+    pub(crate) fn new(config: PoolConfig, client: AsyncSmtpClient<E>) -> Arc<Self> {
         let pool = Arc::new(Self {
             config,
-            connections: Mutex::new(Vec::new()),
+            connections: Mutex::new(Some(Vec::new())),
             client,
-            handle: OnceCell::new(),
+            handle: OnceLock::new(),
         });
 
         {
@@ -61,6 +63,10 @@ impl<E: Executor> Pool<E> {
                             #[allow(clippy::needless_collect)]
                             let (count, dropped) = {
                                 let mut connections = pool.connections.lock().await;
+                                let Some(connections) = connections.as_mut() else {
+                                    // The transport was shut down
+                                    return;
+                                };
 
                                 let to_drop = connections
                                     .iter()
@@ -79,7 +85,7 @@ impl<E: Executor> Pool<E> {
 
                             #[cfg(feature = "tracing")]
                             let mut created = 0;
-                            for _ in count..=(min_idle as usize) {
+                            for _ in count..(min_idle as usize) {
                                 let conn = match pool.client.connection().await {
                                     Ok(conn) => conn,
                                     Err(err) => {
@@ -93,6 +99,11 @@ impl<E: Executor> Pool<E> {
                                 };
 
                                 let mut connections = pool.connections.lock().await;
+                                let Some(connections) = connections.as_mut() else {
+                                    // The transport was shut down
+                                    return;
+                                };
+
                                 connections.push(ParkedConnection::park(conn));
 
                                 #[cfg(feature = "tracing")]
@@ -110,7 +121,7 @@ impl<E: Executor> Pool<E> {
                                 #[cfg(feature = "tracing")]
                                 tracing::debug!("dropped {} idle connections", dropped.len());
 
-                                abort_concurrent(dropped.into_iter().map(|conn| conn.unpark()))
+                                abort_concurrent(dropped.into_iter().map(ParkedConnection::unpark))
                                     .await;
                             }
                         }
@@ -135,10 +146,25 @@ impl<E: Executor> Pool<E> {
         pool
     }
 
-    pub async fn connection(self: &Arc<Self>) -> Result<PooledConnection<E>, Error> {
+    pub(crate) async fn shutdown(&self) {
+        let connections = { self.connections.lock().await.take() };
+        if let Some(connections) = connections {
+            abort_concurrent(connections.into_iter().map(ParkedConnection::unpark)).await;
+        }
+
+        if let Some(handle) = self.handle.get() {
+            handle.shutdown().await;
+        }
+    }
+
+    pub(crate) async fn connection(self: &Arc<Self>) -> Result<PooledConnection<E>, Error> {
         loop {
             let conn = {
                 let mut connections = self.connections.lock().await;
+                let Some(connections) = connections.as_mut() else {
+                    // The transport was shut down
+                    return Err(error::transport_shutdown());
+                };
                 connections.pop()
             };
 
@@ -182,13 +208,20 @@ impl<E: Executor> Pool<E> {
             #[cfg(feature = "tracing")]
             tracing::debug!("recycling connection");
 
-            let mut connections = self.connections.lock().await;
-            if connections.len() >= self.config.max_size as usize {
-                drop(connections);
-                conn.abort().await;
+            let mut connections_guard = self.connections.lock().await;
+
+            if let Some(connections) = connections_guard.as_mut() {
+                if connections.len() >= self.config.max_size as usize {
+                    drop(connections_guard);
+                    conn.abort().await;
+                } else {
+                    let conn = ParkedConnection::park(conn);
+                    connections.push(conn);
+                }
             } else {
-                let conn = ParkedConnection::park(conn);
-                connections.push(conn);
+                // The pool has already been shut down
+                drop(connections_guard);
+                conn.abort().await;
             }
         }
     }
@@ -201,9 +234,15 @@ impl<E: Executor> Debug for Pool<E> {
             .field(
                 "connections",
                 &match self.connections.try_lock() {
-                    Some(connections) => format!("{} connections", connections.len()),
+                    Some(connections) => {
+                        if let Some(connections) = connections.as_ref() {
+                            format!("{} connections", connections.len())
+                        } else {
+                            "SHUT DOWN".to_owned()
+                        }
+                    }
 
-                    None => "LOCKED".to_string(),
+                    None => "LOCKED".to_owned(),
                 },
             )
             .field("client", &self.client)
@@ -223,14 +262,16 @@ impl<E: Executor> Drop for Pool<E> {
         #[cfg(feature = "tracing")]
         tracing::debug!("dropping Pool");
 
-        let connections = mem::take(self.connections.get_mut());
+        let connections = self.connections.get_mut().take();
         let handle = self.handle.take();
         E::spawn(async move {
             if let Some(handle) = handle {
                 handle.shutdown().await;
             }
 
-            abort_concurrent(connections.into_iter().map(|conn| conn.unpark())).await;
+            if let Some(connections) = connections {
+                abort_concurrent(connections.into_iter().map(ParkedConnection::unpark)).await;
+            }
         });
     }
 }

src/transport/smtp/pool/mod.rs

@@ -1,8 +1,8 @@
 use std::time::Duration;
 
 #[cfg(any(feature = "tokio1", feature = "async-std1"))]
-pub mod async_impl;
-pub mod sync_impl;
+pub(super) mod async_impl;
+pub(super) mod sync_impl;
 
 /// Configuration for a connection pool
 #[derive(Debug, Clone)]

src/transport/smtp/pool/sync_impl.rs

@@ -1,8 +1,7 @@
 use std::{
     fmt::{self, Debug},
-    mem,
     ops::{Deref, DerefMut},
-    sync::{Arc, Mutex, TryLockError},
+    sync::{mpsc, Arc, Mutex, TryLockError},
     thread,
     time::{Duration, Instant},
 };
@@ -11,11 +10,12 @@ use super::{
     super::{client::SmtpConnection, Error},
     PoolConfig,
 };
-use crate::transport::smtp::transport::SmtpClient;
+use crate::transport::smtp::{error, transport::SmtpClient};
 
-pub struct Pool {
+pub(crate) struct Pool {
     config: PoolConfig,
-    connections: Mutex<Vec<ParkedConnection>>,
+    connections: Mutex<Option<Vec<ParkedConnection>>>,
+    thread_terminator: mpsc::SyncSender<()>,
     client: SmtpClient,
 }
 
@@ -24,16 +24,19 @@ struct ParkedConnection {
     since: Instant,
 }
 
-pub struct PooledConnection {
+pub(crate) struct PooledConnection {
     conn: Option<SmtpConnection>,
     pool: Arc<Pool>,
 }
 
 impl Pool {
-    pub fn new(config: PoolConfig, client: SmtpClient) -> Arc<Self> {
+    pub(crate) fn new(config: PoolConfig, client: SmtpClient) -> Arc<Self> {
+        let (thread_tx, thread_rx) = mpsc::sync_channel(1);
+
         let pool = Arc::new(Self {
             config,
-            connections: Mutex::new(Vec::new()),
+            connections: Mutex::new(Some(Vec::new())),
+            thread_terminator: thread_tx,
             client,
         });
 
@@ -54,6 +57,10 @@ impl Pool {
                         #[allow(clippy::needless_collect)]
                         let (count, dropped) = {
                             let mut connections = pool.connections.lock().unwrap();
+                            let Some(connections) = connections.as_mut() else {
+                                // The transport was shut down
+                                return;
+                            };
 
                             let to_drop = connections
                                 .iter()
@@ -72,7 +79,7 @@ impl Pool {
 
                         #[cfg(feature = "tracing")]
                         let mut created = 0;
-                        for _ in count..=(min_idle as usize) {
+                        for _ in count..(min_idle as usize) {
                             let conn = match pool.client.connection() {
                                 Ok(conn) => conn,
                                 Err(err) => {
@@ -86,6 +93,11 @@ impl Pool {
                             };
 
                             let mut connections = pool.connections.lock().unwrap();
+                            let Some(connections) = connections.as_mut() else {
+                                // The transport was shut down
+                                return;
+                            };
+
                             connections.push(ParkedConnection::park(conn));
 
                             #[cfg(feature = "tracing")]
@@ -109,7 +121,15 @@ impl Pool {
                             }
                         }
 
-                        thread::sleep(idle_timeout);
+                        drop(pool);
+
+                        match thread_rx.recv_timeout(idle_timeout) {
+                            Ok(()) | Err(mpsc::RecvTimeoutError::Disconnected) => {
+                                // The transport was shut down
+                                return;
+                            }
+                            Err(mpsc::RecvTimeoutError::Timeout) => {}
+                        }
                     }
                 })
                 .expect("couldn't spawn the Pool thread");
@@ -118,10 +138,25 @@ impl Pool {
         pool
     }
 
-    pub fn connection(self: &Arc<Self>) -> Result<PooledConnection, Error> {
+    pub(crate) fn shutdown(&self) {
+        let connections = { self.connections.lock().unwrap().take() };
+        if let Some(connections) = connections {
+            for conn in connections {
+                conn.unpark().abort();
+            }
+        }
+
+        _ = self.thread_terminator.try_send(());
+    }
+
+    pub(crate) fn connection(self: &Arc<Self>) -> Result<PooledConnection, Error> {
         loop {
             let conn = {
                 let mut connections = self.connections.lock().unwrap();
+                let Some(connections) = connections.as_mut() else {
+                    // The transport was shut down
+                    return Err(error::transport_shutdown());
+                };
                 connections.pop()
             };
 
@@ -165,13 +200,20 @@ impl Pool {
             #[cfg(feature = "tracing")]
             tracing::debug!("recycling connection");
 
-            let mut connections = self.connections.lock().unwrap();
-            if connections.len() >= self.config.max_size as usize {
-                drop(connections);
-                conn.abort();
+            let mut connections_guard = self.connections.lock().unwrap();
+
+            if let Some(connections) = connections_guard.as_mut() {
+                if connections.len() >= self.config.max_size as usize {
+                    drop(connections_guard);
+                    conn.abort();
+                } else {
+                    let conn = ParkedConnection::park(conn);
+                    connections.push(conn);
+                }
             } else {
-                let conn = ParkedConnection::park(conn);
-                connections.push(conn);
+                // The pool has already been shut down
+                drop(connections_guard);
+                conn.abort();
             }
         }
     }
@@ -184,10 +226,16 @@ impl Debug for Pool {
             .field(
                 "connections",
                 &match self.connections.try_lock() {
-                    Ok(connections) => format!("{} connections", connections.len()),
+                    Ok(connections) => {
+                        if let Some(connections) = connections.as_ref() {
+                            format!("{} connections", connections.len())
+                        } else {
+                            "SHUT DOWN".to_owned()
+                        }
+                    }
 
-                    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)
@@ -200,10 +248,11 @@ impl Drop for Pool {
         #[cfg(feature = "tracing")]
         tracing::debug!("dropping Pool");
 
-        let connections = mem::take(&mut *self.connections.get_mut().unwrap());
-        for conn in connections {
-            let mut conn = conn.unpark();
-            conn.abort();
+        if let Some(connections) = self.connections.get_mut().unwrap().take() {
+            for conn in connections {
+                let mut conn = conn.unpark();
+                conn.abort();
+            }
         }
     }
 }

src/transport/smtp/response.rs

@@ -5,7 +5,6 @@ use std::{
     fmt::{Display, Formatter, Result},
     result,
     str::FromStr,
-    string::ToString,
 };
 
 use nom::{
@@ -13,13 +12,13 @@ use nom::{
     bytes::streaming::{tag, take_until},
     combinator::{complete, map},
     multi::many0,
-    sequence::{preceded, tuple},
-    IResult,
+    sequence::preceded,
+    IResult, Parser,
 };
 
 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()))
     }
 }
 
@@ -216,7 +221,8 @@ fn parse_severity(i: &str) -> IResult<&str, Severity> {
         map(tag("3"), |_| Severity::PositiveIntermediate),
         map(tag("4"), |_| Severity::TransientNegativeCompletion),
         map(tag("5"), |_| Severity::PermanentNegativeCompletion),
-    ))(i)
+    ))
+    .parse(i)
 }
 
 fn parse_category(i: &str) -> IResult<&str, Category> {
@@ -227,7 +233,8 @@ fn parse_category(i: &str) -> IResult<&str, Category> {
         map(tag("3"), |_| Category::Unspecified3),
         map(tag("4"), |_| Category::Unspecified4),
         map(tag("5"), |_| Category::MailSystem),
-    ))(i)
+    ))
+    .parse(i)
 }
 
 fn parse_detail(i: &str) -> IResult<&str, Detail> {
@@ -242,18 +249,20 @@ fn parse_detail(i: &str) -> IResult<&str, Detail> {
         map(tag("7"), |_| Detail::Seven),
         map(tag("8"), |_| Detail::Eight),
         map(tag("9"), |_| Detail::Nine),
-    ))(i)
+    ))
+    .parse(i)
 }
 
 pub(crate) fn parse_response(i: &str) -> IResult<&str, Response> {
-    let (i, lines) = many0(tuple((
+    let (i, lines) = many0((
         parse_code,
         preceded(tag("-"), take_until("\r\n")),
         tag("\r\n"),
-    )))(i)?;
+    ))
+    .parse(i)?;
     let (i, (last_code, last_line)) =
-        tuple((parse_code, preceded(tag(" "), take_until("\r\n"))))(i)?;
-    let (i, _) = complete(tag("\r\n"))(i)?;
+        (parse_code, preceded(tag(" "), take_until("\r\n"))).parse(i)?;
+    let (i, _) = complete(tag("\r\n")).parse(i)?;
 
     // Check that all codes are equal.
     if !lines.iter().all(|&(code, _, _)| code == last_code) {
@@ -317,6 +326,17 @@ 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 +349,10 @@ 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 +372,7 @@ 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 +381,7 @@ 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 +394,7 @@ 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 +403,7 @@ 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 +417,7 @@ 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 +430,9 @@ 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 +457,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec![" ".to_string()],
+                vec![" ".to_owned()],
             )
             .first_word(),
             None
@@ -469,7 +469,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec!["  ".to_string()],
+                vec!["  ".to_owned()],
             )
             .first_word(),
             None
@@ -481,7 +481,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec!["".to_string()],
+                vec!["".to_owned()],
             )
             .first_word(),
             None
@@ -507,11 +507,7 @@ 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 +520,9 @@ 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 +547,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec![" ".to_string()],
+                vec![" ".to_owned()],
             )
             .first_line(),
             Some(" ")
@@ -563,7 +559,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec!["  ".to_string()],
+                vec!["  ".to_owned()],
             )
             .first_line(),
             Some("  ")
@@ -575,7 +571,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec!["".to_string()],
+                vec!["".to_owned()],
             )
             .first_line(),
             Some("")

src/transport/smtp/transport.rs

@@ -1,17 +1,41 @@
 #[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", feature = "boring-tls"))]
+#[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
 use super::{Tls, TlsParameters, SUBMISSIONS_PORT, SUBMISSION_PORT};
 use crate::{address::Envelope, Transport};
 
-/// Sends emails using the SMTP protocol
+/// Synchronously send emails using the SMTP protocol
+///
+/// `SmtpTransport` is the primary way for communicating
+/// with SMTP relay servers to send email messages. It holds the
+/// client connect configuration and creates new connections
+/// as necessary.
+///
+/// # Connection pool
+///
+/// When the `pool` feature is enabled (default), `SmtpTransport` maintains a
+/// connection pool to manage SMTP connections. The pool:
+///
+/// - Establishes a new connection when sending a message.
+/// - Recycles connections internally after a message is sent.
+/// - Reuses connections for subsequent messages, reducing connection setup overhead.
+///
+/// The connection pool can grow to hold multiple SMTP connections if multiple
+/// emails are sent concurrently, as SMTP does not support multiplexing within a
+/// single connection.
+///
+/// However, **connection reuse is not possible** if the `SmtpTransport` instance
+/// is dropped after every email send operation. You must reuse the instance
+/// of this struct for the connection pool to be of any use.
+///
+/// To customize connection pool settings, use [`SmtpTransportBuilder::pool_config`].
 #[cfg_attr(docsrs, doc(cfg(feature = "smtp-transport")))]
 #[derive(Clone)]
 pub struct SmtpTransport {
@@ -32,10 +56,23 @@ impl Transport for SmtpTransport {
         let result = conn.send(envelope, email)?;
 
         #[cfg(not(feature = "pool"))]
-        conn.quit()?;
+        conn.abort();
 
         Ok(result)
     }
+
+    fn shutdown(&self) {
+        #[cfg(feature = "pool")]
+        self.inner.shutdown();
+    }
+}
+
+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 {
@@ -45,10 +82,10 @@ 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", feature = "boring-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
     #[cfg_attr(
         docsrs,
-        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
     )]
     pub fn relay(relay: &str) -> Result<SmtpTransportBuilder, Error> {
         let tls_parameters = TlsParameters::new(relay.into())?;
@@ -58,7 +95,7 @@ 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.
@@ -69,10 +106,10 @@ 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", feature = "boring-tls"))]
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
     #[cfg_attr(
         docsrs,
-        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
     )]
     pub fn starttls_relay(relay: &str) -> Result<SmtpTransportBuilder, Error> {
         let tls_parameters = TlsParameters::new(relay.into())?;
@@ -95,29 +132,122 @@ 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, port and EHLO name can be provided
+    /// in a single URL. This may be simpler than having to configure SMTP
+    /// through multiple configuration parameters and then having to pass
+    /// those options to lettre.
+    ///
+    /// The URL is created in the following way:
+    /// `scheme://user:pass@hostname:port/ehlo-name?tls=TLS`.
+    ///
+    /// `user` (Username) and `pass` (Password) are optional in case the
+    /// SMTP relay doesn't require authentication. When `port` is not
+    /// configured it is automatically determined based on the `scheme`.
+    /// `ehlo-name` optionally overwrites the hostname sent for the EHLO
+    /// command. `TLS` controls whether STARTTLS is simply enabled
+    /// (`opportunistic` - not enough to prevent man-in-the-middle attacks)
+    /// or `required` (require the server to upgrade the connection to
+    /// STARTTLS, otherwise fail on suspicion of main-in-the-middle attempt).
+    ///
+    /// Use the following table to construct your SMTP url:
+    ///
+    /// | scheme  | `tls` query parameter | example                                            | default port | remarks                                                                                                                               |
+    /// | ------- | --------------------- | -------------------------------------------------- | ------------ | ------------------------------------------------------------------------------------------------------------------------------------- |
+    /// | `smtps` | unset                 | `smtps://user:pass@hostname:port`                  | 465          | SMTP over TLS, recommended method                                                                                                     |
+    /// | `smtp`  | `required`            | `smtp://user:pass@hostname:port?tls=required`      | 587          | SMTP with STARTTLS required, when SMTP over TLS is not available                                                                      |
+    /// | `smtp`  | `opportunistic`       | `smtp://user:pass@hostname:port?tls=opportunistic` | 587          | SMTP with optionally STARTTLS when supported by the server. Not suitable for production use: vulnerable to a man-in-the-middle attack |
+    /// | `smtp`  | unset                 | `smtp://user:pass@hostname:port`                   | 587          | Always unencrypted SMTP. Not suitable for production use: sends all data unencrypted                                                  |
+    ///
+    /// IMPORTANT: some parameters like `user` and `pass` cannot simply
+    /// be concatenated to construct the final URL because special characters
+    /// contained within the parameter may confuse the URL decoder.
+    /// Manually URL encode the parameters before concatenating them or use
+    /// a proper URL encoder, like the following cargo script:
+    ///
+    /// ```rust
+    /// # const TOML: &str = r#"
+    /// #!/usr/bin/env cargo
+    ///
+    /// //! ```cargo
+    /// //! [dependencies]
+    /// //! url = "2"
+    /// //! ```
+    /// # "#;
+    ///
+    /// use url::Url;
+    ///
+    /// fn main() {
+    ///     // don't touch this line
+    ///     let mut url = Url::parse("foo://bar").unwrap();
+    ///
+    ///     // configure the scheme (`smtp` or `smtps`) here.
+    ///     url.set_scheme("smtps").unwrap();
+    ///     // configure the username and password.
+    ///     // remove the following two lines if unauthenticated.
+    ///     url.set_username("username").unwrap();
+    ///     url.set_password(Some("password")).unwrap();
+    ///     // configure the hostname
+    ///     url.set_host(Some("smtp.example.com")).unwrap();
+    ///     // configure the port - only necessary if using a non-default port
+    ///     url.set_port(Some(465)).unwrap();
+    ///     // configure the EHLO name
+    ///     url.set_path("ehlo-name");
+    ///
+    ///     println!("{url}");
+    /// }
+    /// ```
+    ///
+    /// The connection URL can then be used in the following way:
+    ///
+    /// ```rust,no_run
+    /// use lettre::{
+    ///     message::header::ContentType, transport::smtp::authentication::Credentials, Message,
+    ///     SmtpTransport, Transport,
+    /// };
+    ///
+    /// # 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 example
+    /// let mailer = SmtpTransport::from_url("smtps://username:password@smtp.example.com")?.build();
+    ///
+    /// // Send the email
+    /// mailer.send(&email)?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "native-tls", feature = "rustls", 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()?;
 
@@ -141,13 +271,27 @@ 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;
         self
     }
 
-    /// Set the authentication mechanism to use
+    /// Set the authentication credentials to use
     pub fn credentials(mut self, credentials: Credentials) -> Self {
         self.info.credentials = Some(credentials);
         self
@@ -166,16 +310,38 @@ impl SmtpTransportBuilder {
     }
 
     /// Set the port to use
+    ///
+    /// # ⚠️⚠️⚠️ You probably don't need to call this method ⚠️⚠️⚠️
+    ///
+    /// lettre usually picks the correct `port` when building
+    /// [`SmtpTransport`] using [`SmtpTransport::relay`] or
+    /// [`SmtpTransport::starttls_relay`].
+    ///
+    /// # Errors
+    ///
+    /// Using the incorrect `port` and [`Self::tls`] combination may
+    /// lead to hard to debug IO errors coming from the TLS library.
     pub fn port(mut self, port: u16) -> Self {
         self.info.port = port;
         self
     }
 
     /// Set the TLS settings to use
-    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+    ///
+    /// # ⚠️⚠️⚠️ You probably don't need to call this method ⚠️⚠️⚠️
+    ///
+    /// By default lettre chooses the correct `tls` configuration when
+    /// building [`SmtpTransport`] using [`SmtpTransport::relay`] or
+    /// [`SmtpTransport::starttls_relay`].
+    ///
+    /// # Errors
+    ///
+    /// Using the wrong [`Tls`] and [`Self::port`] combination may
+    /// lead to hard to debug IO errors coming from the TLS library.
+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
     #[cfg_attr(
         docsrs,
-        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
+        doc(cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls")))
     )]
     pub fn tls(mut self, tls: Tls) -> Self {
         self.info.tls = tls;
@@ -194,7 +360,7 @@ 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 };
@@ -208,7 +374,7 @@ impl SmtpTransportBuilder {
 
 /// Build client
 #[derive(Debug, Clone)]
-pub struct SmtpClient {
+pub(super) struct SmtpClient {
     info: SmtpInfo,
 }
 
@@ -216,11 +382,11 @@ impl SmtpClient {
     /// Creates a new connection directly usable to send emails
     ///
     /// Handles encryption and authentication
-    pub fn connection(&self) -> Result<SmtpConnection, Error> {
+    pub(super) 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", feature = "boring-tls"))]
-            Tls::Wrapper(ref tls_parameters) => Some(tls_parameters),
+        let tls_parameters = match &self.info.tls {
+            #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
+            Tls::Wrapper(tls_parameters) => Some(tls_parameters),
             _ => None,
         };
 
@@ -233,14 +399,14 @@ impl SmtpClient {
             None,
         )?;
 
-        #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
-        match self.info.tls {
-            Tls::Opportunistic(ref tls_parameters) => {
+        #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
+        match &self.info.tls {
+            Tls::Opportunistic(tls_parameters) => {
                 if conn.can_starttls() {
                     conn.starttls(tls_parameters, &self.info.hello_name)?;
                 }
             }
-            Tls::Required(ref tls_parameters) => {
+            Tls::Required(tls_parameters) => {
                 conn.starttls(tls_parameters, &self.info.hello_name)?;
             }
             _ => (),
@@ -252,3 +418,78 @@ 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

@@ -4,9 +4,9 @@ use std::fmt::{Display, Formatter, Result as FmtResult};
 
 /// Encode a string as xtext
 #[derive(Debug)]
-pub struct XText<'a>(pub &'a str);
+pub(crate) struct XText<'a>(pub(crate) &'a str);
 
-impl<'a> Display for XText<'a> {
+impl Display for XText<'_> {
     fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
         let mut rest = self.0;
         while let Some(idx) = rest.find(|c| c < '!' || c == '+' || c == '=') {
@@ -38,10 +38,8 @@ mod tests {
             ("bjørn", "bjørn"),
             ("Ø+= ❤️‰", "Ø+2B+3D+20❤️‰"),
             ("+", "+2B"),
-        ]
-        .iter()
-        {
-            assert_eq!(format!("{}", XText(input)), (*expect).to_string());
+        ] {
+            assert_eq!(format!("{}", XText(input)), (*expect).to_owned());
         }
     }
 }

src/transport/stub/mod.rs

@@ -11,7 +11,9 @@
 //! ```rust
 //! # #[cfg(feature = "builder")]
 //! # {
-//! use lettre::{transport::stub::StubTransport, Message, Transport};
+//! use lettre::{
+//!     message::header::ContentType, transport::stub::StubTransport, Message, Transport,
+//! };
 //!
 //! # use std::error::Error;
 //! # fn try_main() -> Result<(), Box<dyn Error>> {
@@ -20,11 +22,11 @@
 //!     .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!"))?;
 //!
 //! let mut sender = StubTransport::new_ok();
-//! let result = sender.send(&email);
-//! assert!(result.is_ok());
+//! sender.send(&email)?;
 //! assert_eq!(
 //!     sender.messages(),
 //!     vec![(
@@ -41,13 +43,11 @@
 use std::{
     error::Error as StdError,
     fmt,
-    sync::{Arc, Mutex as StdMutex},
+    sync::{Arc, Mutex},
 };
 
 #[cfg(any(feature = "tokio1", feature = "async-std1"))]
 use async_trait::async_trait;
-#[cfg(any(feature = "tokio1", feature = "async-std1"))]
-use futures_util::lock::Mutex as FuturesMutex;
 
 #[cfg(any(feature = "tokio1", feature = "async-std1"))]
 use crate::AsyncTransport;
@@ -70,7 +70,7 @@ impl StdError for Error {}
 #[derive(Debug, Clone)]
 pub struct StubTransport {
     response: Result<(), Error>,
-    message_log: Arc<StdMutex<Vec<(Envelope, String)>>>,
+    message_log: Arc<Mutex<Vec<(Envelope, String)>>>,
 }
 
 /// This transport logs messages and always returns the given response
@@ -79,7 +79,7 @@ pub struct StubTransport {
 #[cfg_attr(docsrs, doc(cfg(any(feature = "tokio1", feature = "async-std1"))))]
 pub struct AsyncStubTransport {
     response: Result<(), Error>,
-    message_log: Arc<FuturesMutex<Vec<(Envelope, String)>>>,
+    message_log: Arc<Mutex<Vec<(Envelope, String)>>>,
 }
 
 impl StubTransport {
@@ -87,7 +87,7 @@ impl StubTransport {
     pub fn new(response: Result<(), Error>) -> Self {
         Self {
             response,
-            message_log: Arc::new(StdMutex::new(vec![])),
+            message_log: Arc::new(Mutex::new(vec![])),
         }
     }
 
@@ -95,7 +95,7 @@ impl StubTransport {
     pub fn new_ok() -> Self {
         Self {
             response: Ok(()),
-            message_log: Arc::new(StdMutex::new(vec![])),
+            message_log: Arc::new(Mutex::new(vec![])),
         }
     }
 
@@ -103,7 +103,7 @@ impl StubTransport {
     pub fn new_error() -> Self {
         Self {
             response: Err(Error),
-            message_log: Arc::new(StdMutex::new(vec![])),
+            message_log: Arc::new(Mutex::new(vec![])),
         }
     }
 
@@ -122,7 +122,7 @@ impl AsyncStubTransport {
     pub fn new(response: Result<(), Error>) -> Self {
         Self {
             response,
-            message_log: Arc::new(FuturesMutex::new(vec![])),
+            message_log: Arc::new(Mutex::new(vec![])),
         }
     }
 
@@ -130,7 +130,7 @@ impl AsyncStubTransport {
     pub fn new_ok() -> Self {
         Self {
             response: Ok(()),
-            message_log: Arc::new(FuturesMutex::new(vec![])),
+            message_log: Arc::new(Mutex::new(vec![])),
         }
     }
 
@@ -138,14 +138,14 @@ impl AsyncStubTransport {
     pub fn new_error() -> Self {
         Self {
             response: Err(Error),
-            message_log: Arc::new(FuturesMutex::new(vec![])),
+            message_log: Arc::new(Mutex::new(vec![])),
         }
     }
 
     /// Return all logged messages sent using [`AsyncTransport::send_raw`]
     #[cfg(any(feature = "tokio1", feature = "async-std1"))]
     pub async fn messages(&self) -> Vec<(Envelope, String)> {
-        self.message_log.lock().await.clone()
+        self.message_log.lock().unwrap().clone()
     }
 }
 
@@ -171,7 +171,7 @@ impl AsyncTransport for AsyncStubTransport {
     async fn send_raw(&self, envelope: &Envelope, email: &[u8]) -> Result<Self::Ok, Self::Error> {
         self.message_log
             .lock()
-            .await
+            .unwrap()
             .push((envelope.clone(), String::from_utf8_lossy(email).into()));
         self.response
     }