build(deps): upgrade semver compatible dependencies

Prepare v0.11.18 (#1102 )
feat: add ability to give a name to an inline attachment (#1101 )
2025-08-10 19:09:32 +02:00 · 2025-07-28 09:44:38 +02:00 · 2025-07-21 08:19:31 +02:00 · 2025-07-05 12:09:17 +02:00 · 2025-06-05 21:41:17 +02:00 · 2025-06-02 10:43:17 +02:00
48 changed files with 2583 additions and 1122 deletions
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -57,12 +57,12 @@ jobs:

      - 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 }}
@@ -75,8 +75,8 @@ jobs:
            rust: stable
          - name: beta
            rust: beta
-          - name: '1.70'
-            rust: '1.70'
+          - name: '1.74'
+            rust: '1.74'

    steps:
      - name: Checkout
@@ -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
@@ -119,10 +119,10 @@ jobs:
        run: cargo test

      - name: Test with all features (-native-tls)
-        run: cargo test --no-default-features --features async-std1,async-std1-rustls-tls,boring-tls,builder,dkim,file-transport,file-transport-envelope,hostname,mime03,pool,rustls-native-certs,rustls-tls,sendmail-transport,smtp-transport,tokio1,tokio1-boring-tls,tokio1-rustls-tls,tracing
-  
+        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-std1,async-std1-rustls-tls,builder,dkim,file-transport,file-transport-envelope,hostname,mime03,native-tls,pool,rustls-native-certs,rustls-tls,sendmail-transport,smtp-transport,tokio1,tokio1-native-tls,tokio1-rustls-tls,tracing
+        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
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,227 @@
+<a name="v0.11.18"></a>
+### v0.11.18 (2025-07-28)
+
+#### Features
+
+* Allow inline attachments to be named ([#1101])
+
+#### Misc
+
+* Upgrade `socket2` to v0.6 ([#1098])
+
+[#1098]: https://github.com/lettre/lettre/pull/1098
+[#1101]: https://github.com/lettre/lettre/pull/1101
+
+<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)

@@ -508,6 +732,6 @@ 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
--- a/Cargo.lock
+++ b/Cargo.lock
--- a/Cargo.toml
+++ b/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 = "0.11.9"
+version = "0.11.18"
 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 = "1.70"
+rust-version = "1.74"

 [badges]
 is-it-maintained-issue-resolution = { repository = "lettre/lettre" }
@@ -19,9 +19,12 @@ is-it-maintained-open-issues = { repository = "lettre/lettre" }
 maintenance = { status = "actively-developed" }

 [dependencies]
+email_address = { version = "0.2.1", default-features = false }
 chumsky = "0.9"
 idna = "1"
-tracing = { version = "0.1.16", default-features = false, features = ["std"], optional = true } # feature
+
+## tracing support
+tracing = { version = "0.1.16", default-features = false, features = ["std"], optional = true }

 # builder
 httpdate = { version = "1", optional = true }
@@ -29,27 +32,26 @@ mime = { version = "0.3.4", optional = true }
 fastrand = { version = "2.0", optional = true }
 quoted_printable = { version = "0.5", optional = true }
 base64 = { version = "0.22", optional = true }
-email-encoding = { version = "0.3", 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 }
+nom = { version = "8", optional = true }
 hostname = { version = "0.4", optional = true } # feature
-socket2 = { version = "0.5.1", optional = true }
+socket2 = { version = "0.6", optional = true }
 url = { version = "2.4", optional = true }
 percent-encoding = { version = "2.3", optional = true }

 ## tls
-native-tls = { version = "0.2.5", optional = true } # feature
-rustls = { version = "0.23.5", default-features = false, features = ["ring", "logging", "std", "tls12"], optional = true }
-rustls-pemfile = { version = "2", 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 }
-rustls-pki-types = { version = "1.7", optional = true }
-webpki-roots = { version = "0.26", optional = true }
+webpki-roots = { version = "1.0.0", optional = true }
 boring = { version = "4", optional = true }

 # async
@@ -59,21 +61,22 @@ async-trait = { version = "0.1", optional = true }

 ## async-std
 async-std = { version = "1.8", optional = true }
-futures-rustls = { version = "0.26", default-features = false, features = ["logging", "tls12", "ring"], 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 = "0.26", default-features = false, features = ["logging", "tls12", "ring"], 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"] }
+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"
@@ -108,20 +111,33 @@ smtp-transport = ["dep:base64", "dep:nom", "dep:socket2", "dep:url", "dep:percen

 pool = ["dep:futures-util"]

-rustls-tls = ["dep:webpki-roots", "dep:rustls", "dep:rustls-pemfile", "dep:rustls-pki-types"]
+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 = ["dep:boring"]

 # async
 async-std1 = ["dep:async-std", "dep:async-trait", "dep:futures-io", "dep:futures-util"]
-async-std1-rustls-tls = ["async-std1", "rustls-tls", "dep:futures-rustls"]
+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-tls = ["tokio1", "rustls-tls", "dep:tokio1_rustls"]
+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 = ["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)'] }

--- a/2
+++ b/2
@@ -1,5 +1,5 @@
 Copyright (c) 2014-2024 Alexis Mousset <contact@amousset.me>
-Copyright (c) 2019-2024 Paolo Barbolini <paolo@paolo565.org>
+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
--- a/README.md
+++ b/README.md
@@ -28,8 +28,8 @@
 </div>

 <div align="center">
-  <a href="https://deps.rs/crate/lettre/0.11.9">
-    <img src="https://deps.rs/crate/lettre/0.11.9/status.svg"
+  <a href="https://deps.rs/crate/lettre/0.11.18">
+    <img src="https://deps.rs/crate/lettre/0.11.18/status.svg"
      alt="dependency status" />
  </a>
 </div>
@@ -53,12 +53,12 @@ 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 1.70, 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 1.70 or newer.
+This library requires Rust 1.74 or newer.
 To use this library, add the following to your `Cargo.toml`:

 ```toml
@@ -73,9 +73,9 @@ use lettre::{Message, SmtpTransport, Transport};

 fn main() {
    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())
+        .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!"))
@@ -107,7 +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`.
--- a/benches/transport_smtp.rs
+++ b/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));
--- a/clippy.toml
+++ b/clippy.toml
@@ -0,0 +1,3 @@
+disallowed-methods = [
+    { "path" = "std::time::SystemTime::now", reason = "does not work on WASM environments", replacement = "crate::time::now" }
+]
--- a/src/address/envelope.rs
+++ b/src/address/envelope.rs
@@ -29,7 +29,7 @@ pub struct Envelope {
 mod serde_forward_path {
    use super::Address;
    /// dummy type required for serde
-    /// see example: https://serde.rs/deserialize-map.html
+    /// see example: <https://serde.rs/deserialize-map.html>
    struct CustomVisitor;
    impl<'de> serde::de::Visitor<'de> for CustomVisitor {
        type Value = Vec<Address>;
@@ -53,7 +53,7 @@ mod serde_forward_path {
            }
        }
    }
-    pub fn deserialize<'de, D>(deserializer: D) -> Result<Vec<Address>, D::Error>
+    pub(super) fn deserialize<'de, D>(deserializer: D) -> Result<Vec<Address>, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
@@ -163,6 +163,7 @@ impl Envelope {
 }

 #[cfg(feature = "builder")]
+#[cfg_attr(docsrs, doc(cfg(feature = "builder")))]
 impl TryFrom<&Headers> for Envelope {
    type Error = Error;

--- a/src/address/serde.rs
+++ b/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 {
--- a/src/executor.rs
+++ b/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`
@@ -133,7 +134,7 @@ 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"))]
+            #[cfg(any(feature = "tokio1-native-tls", feature = "tokio1-rustls"))]
            Tls::Wrapper(tls_parameters) => Some(tls_parameters.clone()),
            _ => None,
        };
@@ -147,7 +148,7 @@ 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(tls_parameters) => {
                if conn.can_starttls() {
@@ -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, ()>;

@@ -211,7 +212,9 @@ 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")]
@@ -230,7 +233,7 @@ impl Executor for AsyncStd1Executor {
    ) -> Result<AsyncSmtpConnection, Error> {
        #[allow(clippy::match_single_binding)]
        let tls_parameters = match tls {
-            #[cfg(feature = "async-std1-rustls-tls")]
+            #[cfg(feature = "async-std1-rustls")]
            Tls::Wrapper(tls_parameters) => Some(tls_parameters.clone()),
            _ => None,
        };
@@ -243,7 +246,7 @@ impl Executor for AsyncStd1Executor {
        )
        .await?;

-        #[cfg(feature = "async-std1-rustls-tls")]
+        #[cfg(feature = "async-std1-rustls")]
        match tls {
            Tls::Opportunistic(tls_parameters) => {
                if conn.can_starttls() {
@@ -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 {}
 }
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -6,7 +6,7 @@
 //! * Secure defaults
 //! * Async support
 //!
-//! Lettre requires Rust 1.70 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/0.11.9")]
+#![doc(html_root_url = "https://docs.rs/crate/lettre/0.11.18")]
 #![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,
@@ -137,12 +191,36 @@
    clippy::wildcard_imports,
    clippy::str_to_string,
    clippy::empty_structs_with_brackets,
-    clippy::zero_sized_map_values
+    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.");
@@ -153,16 +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(
@@ -171,22 +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",))]
+    #[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.");
 }

@@ -199,6 +273,9 @@ 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;
--- a/src/message/attachment.rs
+++ b/src/message/attachment.rs
@@ -16,7 +16,10 @@ enum Disposition {
    /// File name
    Attached(String),
    /// Content id
-    Inline(String),
+    Inline {
+        content_id: String,
+        name: Option<String>,
+    },
 }

 impl Attachment {
@@ -81,7 +84,50 @@ impl Attachment {
    /// ```
    pub fn new_inline(content_id: String) -> Self {
        Attachment {
-            disposition: Disposition::Inline(content_id),
+            disposition: Disposition::Inline {
+                content_id,
+                name: None,
+            },
+        }
+    }
+
+    /// Create a new inline attachment giving it a name
+    ///
+    /// This attachment should be displayed inline into the message
+    /// body:
+    ///
+    /// ```html
+    /// <img src="cid:123">
+    /// ```
+    ///
+    ///
+    /// ```rust
+    /// # use std::error::Error;
+    /// use std::fs;
+    ///
+    /// use lettre::message::{header::ContentType, Attachment};
+    ///
+    /// # fn main() -> Result<(), Box<dyn Error>> {
+    /// let content_id = String::from("123");
+    /// let file_name = String::from("image.jpg");
+    /// # if false {
+    /// let filebody = fs::read(&file_name)?;
+    /// # }
+    /// # let filebody = fs::read("docs/lettre.png")?;
+    /// let content_type = ContentType::parse("image/jpeg").unwrap();
+    /// let attachment =
+    ///     Attachment::new_inline_with_name(content_id, file_name).body(filebody, content_type);
+    ///
+    /// // The image `attachment` will display inline into the email.
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn new_inline_with_name(content_id: String, name: String) -> Self {
+        Attachment {
+            disposition: Disposition::Inline {
+                content_id,
+                name: Some(name),
+            },
        }
    }

@@ -95,9 +141,18 @@ impl Attachment {
            Disposition::Attached(filename) => {
                builder.header(header::ContentDisposition::attachment(&filename))
            }
-            Disposition::Inline(content_id) => builder
+            Disposition::Inline {
+                content_id,
+                name: None,
+            } => builder
                .header(header::ContentId::from(format!("<{content_id}>")))
                .header(header::ContentDisposition::inline()),
+            Disposition::Inline {
+                content_id,
+                name: Some(name),
+            } => builder
+                .header(header::ContentId::from(format!("<{content_id}>")))
+                .header(header::ContentDisposition::inline_with_name(&name)),
        };
        builder = builder.header(content_type);
        builder.body(content)
@@ -142,4 +197,24 @@ mod tests {
            )
        );
    }
+
+    #[test]
+    fn attachment_inline_with_name() {
+        let id = String::from("id");
+        let name = String::from("test");
+        let part = super::Attachment::new_inline_with_name(id, name).body(
+            String::from("Hello world!"),
+            ContentType::parse("text/plain").unwrap(),
+        );
+        assert_eq!(
+            &String::from_utf8_lossy(&part.formatted()),
+            concat!(
+                "Content-ID: <id>\r\n",
+                "Content-Disposition: inline; filename=\"test\"\r\n",
+                "Content-Type: text/plain\r\n",
+                "Content-Transfer-Encoding: 7bit\r\n\r\n",
+                "Hello world!\r\n"
+            )
+        );
+    }
 }
--- a/src/message/dkim.rs
+++ b/src/message/dkim.rs
@@ -69,7 +69,7 @@ impl Display for DkimSigningAlgorithm {
    }
 }

-/// Describe DkimSigning key error
+/// Describe [`DkimSigningKey`] key error
 #[derive(Debug)]
 pub struct DkimSigningKeyError(InnerDkimSigningKeyError);

@@ -100,7 +100,7 @@ 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);

@@ -183,7 +183,7 @@ impl DkimConfig {
        }
    }

-    /// Create a DkimConfig
+    /// Create a [`DkimConfig`]
    pub fn new(
        selector: String,
        domain: String,
@@ -283,19 +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);
            }
            [] => {}
        }
@@ -317,7 +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,
@@ -344,10 +344,9 @@ fn dkim_canonicalize_headers<'a>(
 }

 /// Sign with Dkim a message by adding Dkim-Signature header created with configuration expressed by
-/// dkim_config
-
+/// `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) {
@@ -378,7 +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,
    );
@@ -488,14 +487,14 @@ cJ5Ku0OTwRtSMaseRPX+T4EfG1Caa/eunPPN4rh+CSup2BVVarOT
    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]
--- a/src/message/header/content_type.rs
+++ b/src/message/header/content_type.rs
@@ -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
--- a/src/message/header/date.rs
+++ b/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())
    }
 }

--- a/src/message/header/mailbox.rs
+++ b/src/message/header/mailbox.rs
@@ -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")
--- a/src/message/header/mod.rs
+++ b/src/message/header/mod.rs
@@ -415,7 +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]
--- a/src/message/mailbox/parsers/rfc2822.rs
+++ b/src/message/mailbox/parsers/rfc2822.rs
@@ -41,14 +41,14 @@ fn quoted_pair() -> impl Parser<char, char, Error = Cheap<char>> {

 // FWS             =       ([*WSP CRLF] 1*WSP) /   ; Folding white space
 //                         obs-FWS
-pub fn fws() -> impl Parser<char, Option<char>, Error = Cheap<char>> {
+pub(super) fn fws() -> impl Parser<char, Option<char>, Error = Cheap<char>> {
    rfc2234::wsp()
        .or_not()
        .then_ignore(rfc2234::wsp().ignored().repeated())
 }

 // CFWS            =       *([FWS] comment) (([FWS] comment) / FWS)
-pub fn cfws() -> impl Parser<char, Option<char>, Error = Cheap<char>> {
+pub(super) fn cfws() -> impl Parser<char, Option<char>, Error = Cheap<char>> {
    // TODO: comment are not currently supported, so for now a cfws is
    // the same as a fws.
    fws()
@@ -106,12 +106,12 @@ pub(super) fn atom() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
 }

 // dot-atom        =       [CFWS] dot-atom-text [CFWS]
-pub fn dot_atom() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+pub(super) fn dot_atom() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
    cfws().chain(dot_atom_text())
 }

 // dot-atom-text   =       1*atext *("." 1*atext)
-pub fn dot_atom_text() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+pub(super) fn dot_atom_text() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
    atext().repeated().at_least(1).chain(
        just('.')
            .chain(atext().repeated().at_least(1))
@@ -204,7 +204,7 @@ pub(crate) fn mailbox_list(
 // https://datatracker.ietf.org/doc/html/rfc2822#section-3.4.1

 // addr-spec       =       local-part "@" domain
-pub fn addr_spec() -> impl Parser<char, (String, String), Error = Cheap<char>> {
+pub(super) fn addr_spec() -> impl Parser<char, (String, String), Error = Cheap<char>> {
    local_part()
        .collect()
        .then_ignore(just('@'))
@@ -212,12 +212,12 @@ pub fn addr_spec() -> impl Parser<char, (String, String), Error = Cheap<char>> {
 }

 // local-part      =       dot-atom / quoted-string / obs-local-part
-pub fn local_part() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+pub(super) fn local_part() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
    choice((dot_atom(), quoted_string(), obs_local_part()))
 }

 // domain          =       dot-atom / domain-literal / obs-domain
-pub fn domain() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+pub(super) fn domain() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
    // NOTE: omitting domain-literal since it may never be used
    choice((dot_atom(), obs_domain()))
 }
@@ -240,11 +240,11 @@ fn obs_phrase() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
 // https://datatracker.ietf.org/doc/html/rfc2822#section-4.4

 // obs-local-part  =       word *("." word)
-pub fn obs_local_part() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+pub(super) fn obs_local_part() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
    word().chain(just('.').chain(word()).repeated().flatten())
 }

 // obs-domain      =       atom *("." atom)
-pub fn obs_domain() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
+pub(super) fn obs_domain() -> impl Parser<char, Vec<char>, Error = Cheap<char>> {
    atom().chain(just('.').chain(atom()).repeated().flatten())
 }
--- a/src/message/mailbox/serde.rs
+++ b/src/message/mailbox/serde.rs
@@ -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 {
--- a/src/message/mailbox/types.rs
+++ b/src/message/mailbox/types.rs
@@ -174,7 +174,7 @@ 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
    ///
@@ -351,7 +351,7 @@ impl FromStr for Mailboxes {
        })?;

        for (name, (user, domain)) in parsed_mailboxes {
-            mailboxes.push(Mailbox::new(name, Address::new(user, domain)?))
+            mailboxes.push(Mailbox::new(name, Address::new(user, domain)?));
        }

        Ok(Mailboxes(mailboxes))
@@ -531,7 +531,7 @@ 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"
        );
--- a/src/message/mod.rs
+++ b/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
@@ -345,7 +345,7 @@ impl MessageBuilder {
                let hostname = hostname::get()
                    .map_err(|_| ())
                    .and_then(|s| s.into_string().map_err(|_| ()))
-                    .unwrap_or_else(|_| DEFAULT_MESSAGE_ID_DOMAIN.to_owned());
+                    .unwrap_or_else(|()| DEFAULT_MESSAGE_ID_DOMAIN.to_owned());
                #[cfg(not(feature = "hostname"))]
                let hostname = DEFAULT_MESSAGE_ID_DOMAIN.to_owned();

@@ -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)))
    }
@@ -527,7 +527,7 @@ impl Message {
        match &self.body {
            MessageBody::Mime(p) => p.format_body(&mut out),
            MessageBody::Raw(r) => out.extend_from_slice(r),
-        };
+        }
        out.extend_from_slice(b"\r\n");
        out
    }
@@ -537,7 +537,10 @@ impl Message {
    /// Example:
    /// ```rust
    /// use lettre::{
-    ///     message::dkim::{DkimConfig, DkimSigningAlgorithm, DkimSigningKey},
+    ///     message::{
+    ///         dkim::{DkimConfig, DkimSigningAlgorithm, DkimSigningKey},
+    ///         header::ContentType,
+    ///     },
    ///     Message,
    /// };
    ///
@@ -546,6 +549,7 @@ impl Message {
    ///     .reply_to("Bob <bob@example.org>".parse().unwrap())
    ///     .to("Carla <carla@example.net>".parse().unwrap())
    ///     .subject("Hello")
+    ///     .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-----
@@ -601,7 +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);
            }
        }
    }
@@ -765,7 +769,7 @@ mod test {
                continue;
            }

-            assert_eq!(line.0, line.1)
+            assert_eq!(line.0, line.1);
        }
    }

--- a/src/rustls_crypto.rs
+++ b/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)
+    })
+}
--- a/src/time.rs
+++ b/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()
+}
--- a/src/transport/file/error.rs
+++ b/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)
    }
@@ -68,7 +69,7 @@ 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(e) = &self.inner.source {
            write!(f, ": {e}")?;
--- a/src/transport/file/mod.rs
+++ b/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!
@@ -167,7 +173,7 @@ pub struct FileTransport {
 }

 /// Asynchronously writes the content and the envelope information to a file
-#[derive(Debug, Clone)]
+#[derive(Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 #[cfg_attr(docsrs, doc(cfg(any(feature = "tokio1", feature = "async-std1"))))]
 #[cfg(any(feature = "async-std1", feature = "tokio1"))]
@@ -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;
--- a/src/transport/mod.rs
+++ b/src/transport/mod.rs
@@ -56,13 +56,17 @@
 //! #
 //! # #[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_owned(), "smtp_password".to_owned());
@@ -136,6 +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
@@ -162,4 +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) {}
 }
--- a/src/transport/sendmail/error.rs
+++ b/src/transport/sendmail/error.rs
@@ -65,7 +65,7 @@ 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(e) = &self.inner.source {
            write!(f, ": {e}")?;
--- a/src/transport/sendmail/mod.rs
+++ b/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(),
--- a/src/transport/smtp/async_transport.rs
+++ b/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>
@@ -81,15 +121,15 @@ where
    /// to validate TLS certificates.
    #[cfg(any(
        feature = "tokio1-native-tls",
-        feature = "tokio1-rustls-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> {
@@ -115,15 +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-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> {
@@ -161,54 +201,72 @@ where

    /// Creates a `AsyncSmtpTransportBuilder` from a connection URL
    ///
-    /// The protocol, credentials, host and port can be provided in a single URL.
-    /// Use the scheme `smtp` for an unencrypted relay (optionally in combination with the
-    /// `tls` parameter to allow/require STARTTLS) or `smtps` for SMTP over TLS.
-    /// The path section of the url can be used to set an alternative name for
-    /// the HELO / EHLO command.
-    /// For example `smtps://username:password@smtp.example.com/client.example.com:465`
-    /// will set the HELO / EHLO name `client.example.com`.
+    /// 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.
    ///
-    /// <table>
-    ///   <thead>
-    ///     <tr>
-    ///       <th>scheme</th>
-    ///       <th>tls parameter</th>
-    ///       <th>example</th>
-    ///       <th>remarks</th>
-    ///     </tr>
-    ///   </thead>
-    ///   <tbody>
-    ///     <tr>
-    ///      <td>smtps</td>
-    ///      <td>-</td>
-    ///      <td>smtps://smtp.example.com</td>
-    ///      <td>SMTP over TLS, recommended method</td>
-    ///     </tr>
-    ///     <tr>
-    ///      <td>smtp</td>
-    ///      <td>required</td>
-    ///      <td>smtp://smtp.example.com?tls=required</td>
-    ///      <td>SMTP with STARTTLS required, when SMTP over TLS is not available</td>
-    ///     </tr>
-    ///     <tr>
-    ///      <td>smtp</td>
-    ///      <td>opportunistic</td>
-    ///      <td>smtp://smtp.example.com?tls=opportunistic</td>
-    ///      <td>
-    ///         SMTP with optionally STARTTLS when supported by the server.
-    ///         Caution: this method is vulnerable to a man-in-the-middle attack.
-    ///         Not recommended for production use.
-    ///       </td>
-    ///     </tr>
-    ///     <tr>
-    ///      <td>smtp</td>
-    ///      <td>-</td>
-    ///      <td>smtp://smtp.example.com</td>
-    ///      <td>Unencrypted SMTP, not recommended for production use.</td>
-    ///     </tr>
-    ///   </tbody>
-    /// </table>
+    /// 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::{
@@ -232,22 +290,18 @@ where
    /// let mailer: AsyncSmtpTransport<Tokio1Executor> =
    ///     AsyncSmtpTransport::<Tokio1Executor>::from_url(
    ///         "smtps://username:password@smtp.example.com:465",
-    ///     )
-    ///     .unwrap()
+    ///     )?
    ///     .build();
    ///
    /// // Send the email
-    /// match mailer.send(email).await {
-    ///     Ok(_) => println!("Email sent successfully!"),
-    ///     Err(e) => panic!("Could not send email: {e:?}"),
-    /// }
+    /// mailer.send(email).await?;
    /// # Ok(())
    /// # }
    /// ```
-    #[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 from_url(connection_url: &str) -> Result<AsyncSmtpTransportBuilder, Error> {
        super::connection_url::from_connection_url(connection_url)
@@ -323,7 +377,7 @@ impl AsyncSmtpTransportBuilder {
        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
@@ -336,6 +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
@@ -348,20 +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-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
    }
@@ -394,7 +470,7 @@ impl AsyncSmtpTransportBuilder {
 }

 /// Build client
-pub struct AsyncSmtpClient<E> {
+pub(super) struct AsyncSmtpClient<E> {
    info: SmtpInfo,
    marker_: PhantomData<E>,
 }
@@ -406,7 +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,
--- a/src/transport/smtp/authentication.rs
+++ b/src/transport/smtp/authentication.rs
@@ -98,13 +98,17 @@ impl Mechanism {
                let decoded_challenge = challenge
                    .ok_or_else(|| error::client("This mechanism does expect a challenge"))?;

-                if ["User Name", "Username:", "Username", "User Name\0"]
-                    .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:", "Password\0"].contains(&decoded_challenge) {
+                if contains_ignore_ascii_case(
+                    decoded_challenge,
+                    ["Password", "Password:", "Password\0"],
+                ) {
                    return Ok(credentials.secret.clone());
                }

@@ -121,6 +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};
@@ -155,6 +168,23 @@ 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;
--- a/src/transport/smtp/client/async_connection.rs
+++ b/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,
@@ -52,10 +54,12 @@ 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
    }
@@ -86,12 +90,12 @@ impl AsyncSmtpConnection {
    ///     Some(TlsParameters::new("example.com".to_owned())?),
    ///     None,
    /// )
-    /// .await
-    /// .unwrap();
+    /// .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>,
@@ -99,6 +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?;
@@ -109,16 +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,
@@ -246,6 +254,7 @@ impl AsyncSmtpConnection {
    }

    /// Sets the underlying stream
+    #[allow(deprecated)]
    pub fn set_stream(&mut self, stream: AsyncNetworkStream) {
        self.stream = BufReader::new(stream);
    }
@@ -369,13 +378,35 @@ 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-tls", feature = "boring-tls"))]
+    #[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()
    }
--- a/src/transport/smtp/client/async_net.rs
+++ b/src/transport/smtp/client/async_net.rs
@@ -9,12 +9,12 @@ use std::{
 #[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(any(feature = "tokio1-rustls-tls", feature = "async-std1-rustls-tls"))]
+#[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;
@@ -27,14 +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-rustls-tls"
+    feature = "async-std1-rustls"
 ))]
 use super::InnerTlsParameters;
 use super::TlsParameters;
@@ -44,6 +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,
 }
@@ -74,8 +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>>),
@@ -83,12 +87,13 @@ enum InnerAsyncNetworkStream {
    #[cfg(feature = "async-std1")]
    AsyncStd1Tcp(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 {
@@ -107,18 +112,17 @@ impl AsyncNetworkStream {
            InnerAsyncNetworkStream::Tokio1NativeTls(s) => {
                s.get_ref().get_ref().get_ref().peer_addr()
            }
-            #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(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(s) => s.get_ref().peer_addr(),
            #[cfg(feature = "async-std1")]
            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => s.peer_addr(),
-            #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => s.get_ref().0.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",
                ))
            }
@@ -126,11 +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>,
@@ -170,7 +176,7 @@ impl AsyncNetworkStream {
                            last_err = Some(io::Error::new(
                                io::ErrorKind::TimedOut,
                                "connection timed out",
-                            ))
+                            ));
                        }
                    }
                } else {
@@ -197,6 +203,7 @@ 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>,
@@ -222,7 +229,7 @@ impl AsyncNetworkStream {
                        last_err = Some(io::Error::new(
                            io::ErrorKind::TimedOut,
                            "connection timed out",
-                        ))
+                        ));
                    }
                }
            }
@@ -253,26 +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)
@@ -280,19 +286,18 @@ impl AsyncNetworkStream {
                    .map_err(error::connection)?;
                Ok(())
            }
-            #[cfg(all(feature = "async-std1", not(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 the async-std1-rustls-tls feature");
+                panic!("Trying to upgrade an AsyncNetworkStream without having enabled the async-std1-rustls feature");
            }

-            #[cfg(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)
@@ -307,7 +312,7 @@ 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(
@@ -318,7 +323,7 @@ impl AsyncNetworkStream {

        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");

@@ -334,12 +339,12 @@ 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 tokio1_rustls::TlsConnector;

@@ -351,18 +356,21 @@ impl AsyncNetworkStream {
                        .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
@@ -374,7 +382,7 @@ impl AsyncNetworkStream {
    }

    #[allow(unused_variables)]
-    #[cfg(feature = "async-std1-rustls-tls")]
+    #[cfg(feature = "async-std1-rustls")]
    async fn upgrade_asyncstd1_tls(
        tcp_stream: AsyncStd1TcpStream,
        mut tls_parameters: TlsParameters,
@@ -383,15 +391,15 @@ 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(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;

@@ -403,11 +411,11 @@ impl AsyncNetworkStream {
                        .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.");
            }
        }
@@ -419,18 +427,44 @@ impl AsyncNetworkStream {
            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-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")]
@@ -439,8 +473,8 @@ impl AsyncNetworkStream {
            }
            #[cfg(feature = "tokio1-native-tls")]
            InnerAsyncNetworkStream::Tokio1NativeTls(_) => panic!("Unsupported"),
-            #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(stream) => Ok(stream
+            #[cfg(feature = "tokio1-rustls")]
+            InnerAsyncNetworkStream::Tokio1Rustls(stream) => Ok(stream
                .get_ref()
                .1
                .peer_certificates()
@@ -460,8 +494,8 @@ impl AsyncNetworkStream {
            InnerAsyncNetworkStream::AsyncStd1Tcp(_) => {
                Err(error::client("Connection is not encrypted"))
            }
-            #[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()
@@ -487,8 +521,8 @@ 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()
@@ -507,8 +541,8 @@ impl AsyncNetworkStream {
            InnerAsyncNetworkStream::AsyncStd1Tcp(_) => {
                Err(error::client("Connection is not encrypted"))
            }
-            #[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()
@@ -521,6 +555,7 @@ impl AsyncNetworkStream {
    }
 }

+#[allow(deprecated)]
 impl FuturesAsyncRead for AsyncNetworkStream {
    fn poll_read(
        mut self: Pin<&mut Self>,
@@ -546,8 +581,8 @@ impl FuturesAsyncRead for AsyncNetworkStream {
                    Poll::Pending => Poll::Pending,
                }
            }
-            #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(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())),
@@ -566,8 +601,8 @@ impl FuturesAsyncRead for AsyncNetworkStream {
            }
            #[cfg(feature = "async-std1")]
            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => Pin::new(s).poll_read(cx, buf),
-            #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(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))
@@ -576,6 +611,7 @@ impl FuturesAsyncRead for AsyncNetworkStream {
    }
 }

+#[allow(deprecated)]
 impl FuturesAsyncWrite for AsyncNetworkStream {
    fn poll_write(
        mut self: Pin<&mut Self>,
@@ -587,14 +623,14 @@ impl FuturesAsyncWrite for AsyncNetworkStream {
            InnerAsyncNetworkStream::Tokio1Tcp(s) => Pin::new(s).poll_write(cx, buf),
            #[cfg(feature = "tokio1-native-tls")]
            InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_write(cx, buf),
-            #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(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(s) => Pin::new(s).poll_write(cx, buf),
            #[cfg(feature = "async-std1")]
            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => Pin::new(s).poll_write(cx, buf),
-            #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(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))
@@ -608,14 +644,14 @@ impl FuturesAsyncWrite for AsyncNetworkStream {
            InnerAsyncNetworkStream::Tokio1Tcp(s) => Pin::new(s).poll_flush(cx),
            #[cfg(feature = "tokio1-native-tls")]
            InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_flush(cx),
-            #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(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(s) => Pin::new(s).poll_flush(cx),
            #[cfg(feature = "async-std1")]
            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => Pin::new(s).poll_flush(cx),
-            #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(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(()))
@@ -629,14 +665,14 @@ impl FuturesAsyncWrite for AsyncNetworkStream {
            InnerAsyncNetworkStream::Tokio1Tcp(s) => Pin::new(s).poll_shutdown(cx),
            #[cfg(feature = "tokio1-native-tls")]
            InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_shutdown(cx),
-            #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(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(s) => Pin::new(s).poll_shutdown(cx),
            #[cfg(feature = "async-std1")]
            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => Pin::new(s).poll_close(cx),
-            #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(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(()))
--- a/src/transport/smtp/client/connection.rs
+++ b/src/transport/smtp/client/connection.rs
@@ -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");
@@ -303,13 +299,35 @@ 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-tls", feature = "boring-tls"))]
+    #[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()
    }
--- a/src/transport/smtp/client/mod.rs
+++ b/src/transport/smtp/client/mod.rs
@@ -28,13 +28,14 @@ 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,
@@ -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,
        }
--- a/src/transport/smtp/client/net.rs
+++ b/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")]
+#[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
@@ -59,8 +59,8 @@ impl NetworkStream {
            InnerNetworkStream::Tcp(s) => s.peer_addr(),
            #[cfg(feature = "native-tls")]
            InnerNetworkStream::NativeTls(s) => s.get_ref().peer_addr(),
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(s) => s.get_ref().peer_addr(),
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(s) => s.get_ref().peer_addr(),
            #[cfg(feature = "boring-tls")]
            InnerNetworkStream::BoringTls(s) => s.get_ref().peer_addr(),
            InnerNetworkStream::None => {
@@ -79,8 +79,8 @@ impl NetworkStream {
            InnerNetworkStream::Tcp(s) => s.shutdown(how),
            #[cfg(feature = "native-tls")]
            InnerNetworkStream::NativeTls(s) => s.get_ref().shutdown(how),
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(s) => s.get_ref().shutdown(how),
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(s) => s.get_ref().shutdown(how),
            #[cfg(feature = "boring-tls")]
            InnerNetworkStream::BoringTls(s) => s.get_ref().shutdown(how),
            InnerNetworkStream::None => {
@@ -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.to_owned())
+                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)
@@ -212,8 +210,8 @@ impl NetworkStream {
            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 => {
@@ -223,14 +221,32 @@ impl NetworkStream {
        }
    }

-    #[cfg(any(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-tls")]
-            InnerNetworkStream::RustlsTls(stream) => Ok(stream
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(stream) => Ok(stream
                .conn
                .peer_certificates()
                .unwrap()
@@ -249,7 +265,11 @@ impl NetworkStream {
        }
    }

-    #[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> {
        match &self.inner {
            InnerNetworkStream::Tcp(_) => Err(error::client("Connection is not encrypted")),
@@ -260,8 +280,8 @@ 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()
@@ -284,8 +304,8 @@ impl NetworkStream {
            InnerNetworkStream::Tcp(stream) => stream.set_read_timeout(duration),
            #[cfg(feature = "native-tls")]
            InnerNetworkStream::NativeTls(stream) => stream.get_ref().set_read_timeout(duration),
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(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(stream) => stream.get_ref().set_read_timeout(duration),
            InnerNetworkStream::None => {
@@ -302,8 +322,8 @@ impl NetworkStream {

            #[cfg(feature = "native-tls")]
            InnerNetworkStream::NativeTls(stream) => stream.get_ref().set_write_timeout(duration),
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(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(stream) => stream.get_ref().set_write_timeout(duration),
            InnerNetworkStream::None => {
@@ -320,8 +340,8 @@ impl Read for NetworkStream {
            InnerNetworkStream::Tcp(s) => s.read(buf),
            #[cfg(feature = "native-tls")]
            InnerNetworkStream::NativeTls(s) => s.read(buf),
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(s) => s.read(buf),
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(s) => s.read(buf),
            #[cfg(feature = "boring-tls")]
            InnerNetworkStream::BoringTls(s) => s.read(buf),
            InnerNetworkStream::None => {
@@ -338,8 +358,8 @@ impl Write for NetworkStream {
            InnerNetworkStream::Tcp(s) => s.write(buf),
            #[cfg(feature = "native-tls")]
            InnerNetworkStream::NativeTls(s) => s.write(buf),
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(s) => s.write(buf),
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(s) => s.write(buf),
            #[cfg(feature = "boring-tls")]
            InnerNetworkStream::BoringTls(s) => s.write(buf),
            InnerNetworkStream::None => {
@@ -354,8 +374,8 @@ impl Write for NetworkStream {
            InnerNetworkStream::Tcp(s) => s.flush(),
            #[cfg(feature = "native-tls")]
            InnerNetworkStream::NativeTls(s) => s.flush(),
-            #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(s) => s.flush(),
+            #[cfg(feature = "rustls")]
+            InnerNetworkStream::Rustls(s) => s.flush(),
            #[cfg(feature = "boring-tls")]
            InnerNetworkStream::BoringTls(s) => s.flush(),
            InnerNetworkStream::None => {
@@ -369,7 +389,7 @@ 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 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,
--- a/src/transport/smtp/client/tls.rs
+++ b/src/transport/smtp/client/tls.rs
@@ -1,6 +1,6 @@
 use std::fmt::{self, Debug};
-#[cfg(feature = "rustls-tls")]
-use std::{io, sync::Arc};
+#[cfg(feature = "rustls")]
+use std::sync::Arc;

 #[cfg(feature = "boring-tls")]
 use boring::{
@@ -10,23 +10,22 @@ use boring::{
 };
 #[cfg(feature = "native-tls")]
 use native_tls::{Protocol, TlsConnector};
-#[cfg(feature = "rustls-tls")]
+#[cfg(feature = "rustls")]
 use rustls::{
    client::danger::{HandshakeSignatureValid, ServerCertVerified, ServerCertVerifier},
-    crypto::WebPkiSupportedAlgorithms,
-    crypto::{verify_tls12_signature, verify_tls13_signature},
-    pki_types::{CertificateDer, PrivateKeyDer, ServerName, UnixTime},
+    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
    ///
@@ -59,31 +58,75 @@ pub enum TlsVersion {
    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),
 }
@@ -92,11 +135,11 @@ 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"),
        }
    }
@@ -105,14 +148,25 @@ impl Debug for Tls {
 /// 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 also use the system store if the `rustls-native-certs` feature is
-    /// enabled, or will fall back to `webpki-roots`.
+    /// 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]
@@ -120,7 +174,7 @@ pub enum CertificateStore {
    /// Use a hardcoded set of Mozilla roots via the `webpki-roots` crate.
    ///
    /// This option is only available in the rustls backend.
-    #[cfg(feature = "rustls-tls")]
+    #[cfg(all(feature = "rustls", feature = "webpki-roots"))]
    WebpkiRoots,
    /// Don't use any system certificates.
    None,
@@ -128,16 +182,34 @@ pub enum CertificateStore {

 /// 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,
@@ -145,7 +217,7 @@ pub struct TlsParametersBuilder {
    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,
 }

@@ -159,7 +231,7 @@ impl TlsParametersBuilder {
            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,
        }
    }
@@ -188,6 +260,8 @@ impl TlsParametersBuilder {

    /// Controls whether certificates with an invalid hostname are accepted
    ///
+    /// This option is silently disabled when using `rustls-platform-verifier`.
+    ///
    /// Defaults to `false`.
    ///
    /// # Warning
@@ -197,10 +271,10 @@ impl TlsParametersBuilder {
    /// including those from other sites, are trusted.
    ///
    /// This method introduces significant vulnerabilities to man-in-the-middle 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 dangerous_accept_invalid_hostnames(mut self, accept_invalid_hostnames: bool) -> Self {
        self.accept_invalid_hostnames = accept_invalid_hostnames;
@@ -210,7 +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
@@ -239,17 +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();
    }

@@ -295,10 +373,8 @@ impl TlsParametersBuilder {

        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,
        })
    }

@@ -356,15 +432,17 @@ 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 just_version3 = &[&rustls::version::TLS13];
        let supported_versions = match self.min_tls_version {
@@ -378,18 +456,19 @@ impl TlsParametersBuilder {
            TlsVersion::Tlsv13 => just_version3,
        };

-        let tls = ClientConfig::builder_with_protocol_versions(supported_versions);
-        let provider = rustls::crypto::CryptoProvider::get_default()
-            .cloned()
-            .unwrap_or_else(|| Arc::new(rustls::crypto::ring::default_provider()));
+        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)?;

        // Build TLS config
-        let signature_algorithms = provider.signature_verification_algorithms;
-
        let mut root_cert_store = RootCertStore::empty();

-        #[cfg(feature = "rustls-native-certs")]
-        fn load_native_roots(store: &mut RootCertStore) -> Result<(), Error> {
+        #[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();
@@ -399,22 +478,38 @@ impl TlsParametersBuilder {
            tracing::debug!(
                "loaded platform certs with {errors_len} failing to load, {added} valid and {ignored} ignored (invalid) certs"
            );
-            Ok(())
+            #[cfg(not(feature = "tracing"))]
+            let _ = (errors_len, added, ignored);
        }

-        #[cfg(feature = "rustls-tls")]
+        #[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-native-certs")]
-                load_native_roots(&mut root_cert_store)?;
-                #[cfg(not(feature = "rustls-native-certs"))]
+                #[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(feature = "rustls-tls")]
+            #[cfg(all(feature = "rustls", feature = "webpki-roots"))]
            CertificateStore::WebpkiRoots => {
                load_webpki_roots(&mut root_cert_store);
            }
@@ -422,21 +517,43 @@ impl TlsParametersBuilder {
        }
        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 || self.accept_invalid_hostnames {
+        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,
-                signature_algorithms,
+                crypto_provider,
            };
            tls.dangerous()
                .with_custom_certificate_verifier(Arc::new(verifier))
        } else {
-            tls.with_root_certificates(root_cert_store)
+            #[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 {
@@ -448,32 +565,35 @@ impl TlsParametersBuilder {
        };

        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()
@@ -492,8 +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()
    }
@@ -513,16 +633,26 @@ impl TlsParameters {
 /// 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")]
+    #[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> {
@@ -535,7 +665,7 @@ impl Certificate {
        Ok(Self {
            #[cfg(feature = "native-tls")]
            native_tls: native_tls_cert,
-            #[cfg(feature = "rustls-tls")]
+            #[cfg(feature = "rustls")]
            rustls: vec![der.into()],
            #[cfg(feature = "boring-tls")]
            boring_tls: boring_tls_cert,
@@ -550,20 +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)
-                .collect::<io::Result<Vec<_>>>()
+            CertificateDer::pem_slice_iter(pem)
+                .collect::<Result<Vec<_>, pki_types::pem::Error>>()
                .map_err(|_| error::tls("invalid certificates"))?
        };

        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,
@@ -579,10 +706,20 @@ impl Debug for Certificate {

 /// 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-tls")]
+    #[cfg(feature = "rustls")]
    rustls_tls: (Vec<CertificateDer<'static>>, PrivateKeyDer<'static>),
    #[cfg(feature = "boring-tls")]
    boring_tls: (boring::x509::X509, PKey<boring::pkey::Private>),
@@ -599,7 +736,7 @@ impl Clone for Identity {
        Identity {
            #[cfg(feature = "native-tls")]
            native_tls: self.native_tls.clone(),
-            #[cfg(feature = "rustls-tls")]
+            #[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()),
@@ -607,13 +744,13 @@ impl Clone for Identity {
    }
 }

-#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+#[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-tls")]
+            #[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)?,
@@ -625,13 +762,19 @@ impl Identity {
        native_tls::Identity::from_pkcs8(pem, key).map_err(error::tls)
    }

-    #[cfg(feature = "rustls-tls")]
+    #[cfg(feature = "rustls")]
    fn from_pem_rustls_tls(
        pem: &[u8],
        key: &[u8],
    ) -> Result<(Vec<CertificateDer<'static>>, PrivateKeyDer<'static>), Error> {
-        let mut key = key;
-        let key = rustls_pemfile::private_key(&mut key).unwrap().unwrap();
+        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))
    }

@@ -646,16 +789,16 @@ impl Identity {
    }
 }

-#[cfg(feature = "rustls-tls")]
+#[cfg(feature = "rustls")]
 #[derive(Debug)]
 struct InvalidCertsVerifier {
    ignore_invalid_hostnames: bool,
    ignore_invalid_certs: bool,
    roots: RootCertStore,
-    signature_algorithms: WebPkiSupportedAlgorithms,
+    crypto_provider: Arc<CryptoProvider>,
 }

-#[cfg(feature = "rustls-tls")]
+#[cfg(feature = "rustls")]
 impl ServerCertVerifier for InvalidCertsVerifier {
    fn verify_server_cert(
        &self,
@@ -673,7 +816,7 @@ impl ServerCertVerifier for InvalidCertsVerifier {
                &self.roots,
                intermediates,
                now,
-                self.signature_algorithms.all,
+                self.crypto_provider.signature_verification_algorithms.all,
            )?;
        }

@@ -693,7 +836,7 @@ impl ServerCertVerifier for InvalidCertsVerifier {
            message,
            cert,
            dss,
-            &rustls::crypto::ring::default_provider().signature_verification_algorithms,
+            &self.crypto_provider.signature_verification_algorithms,
        )
    }

@@ -707,12 +850,12 @@ impl ServerCertVerifier for InvalidCertsVerifier {
            message,
            cert,
            dss,
-            &rustls::crypto::ring::default_provider().signature_verification_algorithms,
+            &self.crypto_provider.signature_verification_algorithms,
        )
    }

    fn supported_verify_schemes(&self) -> Vec<SignatureScheme> {
-        rustls::crypto::ring::default_provider()
+        self.crypto_provider
            .signature_verification_algorithms
            .supported_schemes()
    }
--- a/src/transport/smtp/connection_url.rs
+++ b/src/transport/smtp/connection_url.rs
@@ -1,6 +1,8 @@
+use std::borrow::Cow;
+
 use url::Url;

-#[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+#[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;
@@ -11,6 +13,7 @@ use super::{

 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;
@@ -22,6 +25,7 @@ impl TransportBuilder for SmtpTransportBuilder {
        Self::new(server)
    }

+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
    fn tls(self, tls: super::Tls) -> Self {
        self.tls(tls)
    }
@@ -45,6 +49,7 @@ impl TransportBuilder for AsyncSmtpTransportBuilder {
        Self::new(server)
    }

+    #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
    fn tls(self, tls: super::Tls) -> Self {
        self.tls(tls)
    }
@@ -62,7 +67,7 @@ impl TransportBuilder for AsyncSmtpTransportBuilder {
    }
 }

-/// Create a new SmtpTransportBuilder or AsyncSmtpTransportBuilder from a connection URL
+/// 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
@@ -80,30 +85,30 @@ pub(crate) fn from_connection_url<B: TransportBuilder>(connection_url: &str) ->
        ("smtp", None) => {
            builder = builder.port(connection_url.port().unwrap_or(SMTP_PORT));
        }
-        #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+        #[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())?))
+                .tls(Tls::Required(TlsParameters::new(host.into())?));
        }
-        #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+        #[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())?))
+                .tls(Tls::Opportunistic(TlsParameters::new(host.into())?));
        }
-        #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+        #[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())?))
+                .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 {
@@ -115,7 +120,7 @@ pub(crate) fn from_connection_url<B: TransportBuilder>(connection_url: &str) ->
        let percent_decode = |s: &str| {
            percent_encoding::percent_decode_str(s)
                .decode_utf8()
-                .map(|cow| cow.into_owned())
+                .map(Cow::into_owned)
                .map_err(error::connection)
        };
        let credentials = Credentials::new(
--- a/src/transport/smtp/error.rs
+++ b/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 {
@@ -134,15 +141,16 @@ impl fmt::Display for 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::TransportShutdown => f.write_str("transport has been shut down")?,
            Kind::Transient(code) => {
                write!(f, "transient error ({code})")?;
            }
            Kind::Permanent(code) => {
                write!(f, "permanent error ({code})")?;
            }
-        };
+        }

        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)
+}
--- a/src/transport/smtp/extension.rs
+++ b/src/transport/smtp/extension.rs
@@ -129,9 +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();
@@ -169,7 +168,7 @@ impl ServerInfo {
                    }
                }
                _ => (),
-            };
+            }
        }

        Ok(ServerInfo {
--- a/src/transport/smtp/mod.rs
+++ b/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_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_owned())
-//!     .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},
--- a/src/transport/smtp/pool/async_impl.rs
+++ b/src/transport/smtp/pool/async_impl.rs
@@ -1,6 +1,5 @@
 use std::{
    fmt::{self, Debug},
-    mem,
    ops::{Deref, DerefMut},
    sync::{Arc, OnceLock},
    time::{Duration, Instant},
@@ -15,11 +14,15 @@ 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: OnceLock<E::Handle>,
 }
@@ -29,16 +32,16 @@ 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: OnceLock::new(),
        });
@@ -60,6 +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()
@@ -78,7 +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) => {
@@ -92,6 +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")]
@@ -109,7 +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;
                            }
                        }
@@ -134,10 +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()
            };

@@ -181,13 +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;
            }
        }
    }
@@ -200,7 +234,13 @@ 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_owned(),
                },
@@ -222,14 +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;
+            }
        });
    }
 }
--- a/src/transport/smtp/pool/mod.rs
+++ b/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)]
--- a/src/transport/smtp/pool/sync_impl.rs
+++ b/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();
            }
        }
    }
@@ -184,7 +226,13 @@ 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_owned(),
                    Err(TryLockError::Poisoned(_)) => "POISONED".to_owned(),
@@ -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();
+            }
        }
    }
 }
--- a/src/transport/smtp/response.rs
+++ b/src/transport/smtp/response.rs
@@ -12,8 +12,8 @@ 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};
@@ -221,7 +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> {
@@ -232,7 +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> {
@@ -247,18 +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) {
--- a/src/transport/smtp/transport.rs
+++ b/src/transport/smtp/transport.rs
@@ -7,11 +7,35 @@ 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 +56,15 @@ 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 {
@@ -53,10 +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())?;
@@ -77,10 +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())?;
@@ -115,54 +144,72 @@ impl SmtpTransport {

    /// Creates a `SmtpTransportBuilder` from a connection URL
    ///
-    /// The protocol, credentials, host and port can be provided in a single URL.
-    /// Use the scheme `smtp` for an unencrypted relay (optionally in combination with the
-    /// `tls` parameter to allow/require STARTTLS) or `smtps` for SMTP over TLS.
-    /// The path section of the url can be used to set an alternative name for
-    /// the HELO / EHLO command.
-    /// For example `smtps://username:password@smtp.example.com/client.example.com:465`
-    /// will set the HELO / EHLO name `client.example.com`.
+    /// 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.
    ///
-    /// <table>
-    ///   <thead>
-    ///     <tr>
-    ///       <th>scheme</th>
-    ///       <th>tls parameter</th>
-    ///       <th>example</th>
-    ///       <th>remarks</th>
-    ///     </tr>
-    ///   </thead>
-    ///   <tbody>
-    ///     <tr>
-    ///      <td>smtps</td>
-    ///      <td>-</td>
-    ///      <td>smtps://smtp.example.com</td>
-    ///      <td>SMTP over TLS, recommended method</td>
-    ///     </tr>
-    ///     <tr>
-    ///      <td>smtp</td>
-    ///      <td>required</td>
-    ///      <td>smtp://smtp.example.com?tls=required</td>
-    ///      <td>SMTP with STARTTLS required, when SMTP over TLS is not available</td>
-    ///     </tr>
-    ///     <tr>
-    ///      <td>smtp</td>
-    ///      <td>opportunistic</td>
-    ///      <td>smtp://smtp.example.com?tls=opportunistic</td>
-    ///      <td>
-    ///         SMTP with optionally STARTTLS when supported by the server.
-    ///         Caution: this method is vulnerable to a man-in-the-middle attack.
-    ///         Not recommended for production use.
-    ///       </td>
-    ///     </tr>
-    ///     <tr>
-    ///      <td>smtp</td>
-    ///      <td>-</td>
-    ///      <td>smtp://smtp.example.com</td>
-    ///      <td>Unencrypted SMTP, not recommended for production use.</td>
-    ///     </tr>
-    ///   </tbody>
-    /// </table>
+    /// 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::{
@@ -170,6 +217,7 @@ impl SmtpTransport {
    ///     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())
@@ -180,20 +228,17 @@ impl SmtpTransport {
    ///     .unwrap();
    ///
    /// // Open a remote connection to example
-    /// let mailer = SmtpTransport::from_url("smtps://username:password@smtp.example.com:465")
-    ///     .unwrap()
-    ///     .build();
+    /// let mailer = SmtpTransport::from_url("smtps://username:password@smtp.example.com")?.build();
    ///
    /// // Send the email
-    /// match mailer.send(&email) {
-    ///     Ok(_) => println!("Email sent successfully!"),
-    ///     Err(e) => panic!("Could not send email: {e:?}"),
-    /// }
+    /// mailer.send(&email)?;
+    /// # Ok(())
+    /// # }
    /// ```
-    #[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 from_url(connection_url: &str) -> Result<SmtpTransportBuilder, Error> {
        super::connection_url::from_connection_url(connection_url)
@@ -246,7 +291,7 @@ impl SmtpTransportBuilder {
        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
@@ -265,16 +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;
@@ -307,7 +374,7 @@ impl SmtpTransportBuilder {

 /// Build client
 #[derive(Debug, Clone)]
-pub struct SmtpClient {
+pub(super) struct SmtpClient {
    info: SmtpInfo,
 }

@@ -315,10 +382,10 @@ 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"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
            Tls::Wrapper(tls_parameters) => Some(tls_parameters),
            _ => None,
        };
@@ -332,7 +399,7 @@ impl SmtpClient {
            None,
        )?;

-        #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+        #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
        match &self.info.tls {
            Tls::Opportunistic(tls_parameters) => {
                if conn.can_starttls() {
--- a/src/transport/smtp/util.rs
+++ b/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 == '=') {
@@ -38,9 +38,7 @@ mod tests {
            ("bjørn", "bjørn"),
            ("Ø+= ❤️‰", "Ø+2B+3D+20❤️‰"),
            ("+", "+2B"),
-        ]
-        .iter()
-        {
+        ] {
            assert_eq!(format!("{}", XText(input)), (*expect).to_owned());
        }
    }
--- a/src/transport/stub/mod.rs
+++ b/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
    }
Author	SHA1	Message	Date
Paolo Barbolini	fb33215a00	build(deps): upgrade semver compatible dependencies	2025-08-10 19:09:32 +02:00
Paolo Barbolini	3d16344d53	Prepare v0.11.18 (#1102 )	2025-07-28 09:44:38 +02:00
Francesco Luzzi	8873153178	feat: add ability to give a name to an inline attachment (#1101 )	2025-07-21 08:19:31 +02:00
Paolo Barbolini	b073df7666	build(deps): upgrade socket2 to v0.6 (#1098 )	2025-07-05 12:09:17 +02:00
Paolo Barbolini	cf6b767a9c	Prepare v0.11.17 (#1093 )	2025-06-05 21:41:17 +02:00
Paolo Barbolini	d3d8e24824	feat: add `rustls-platform-verifier` support (#1081 )	2025-06-02 10:43:17 +02:00
Paolo Barbolini	c4df9730aa	refactor(smtp/pool): remove duplicate abort_concurrent implementation (#1092 )	2025-05-24 16:37:54 +02:00
Paolo Barbolini	bfed19e6ad	refactor(stub): always use std Mutex (#1091 )	2025-05-24 14:34:09 +00:00
David Campbell	629967ac98	docs: use `Mailbox::new` rather than string parsing (#1090 )	2025-05-24 16:21:15 +02:00
Paolo Barbolini	06e381ec9c	Prepare v0.11.16 (#1089 )	2025-05-12 11:16:14 +02:00
Paolo Barbolini	d9ce9a6e47	chore: deprecate ungated TLS types _when_ no TLS backend is enabled (#1084 )	2025-05-11 09:36:47 +02:00
Paolo Barbolini	e892b55b6b	build(deps): upgrade webpki-roots to v1 (#1088 )	2025-05-06 12:37:39 +00:00
Paolo Barbolini	771d212198	build: gate `web-time` behind `cfg(target_arch = "wasm32")` (#1086 )	2025-05-01 18:32:26 +02:00
Paolo Barbolini	83ba93944d	docs: add missing `doc(cfg(...))` attributes (#1085 )	2025-05-01 18:16:40 +02:00
Paolo Barbolini	de3ab006e2	fix: feature gate internal `TransportBuilder::tls` to avoid recursive call site (#1083 )	2025-05-01 15:09:07 +02:00
Paolo Barbolini	9504b7f45c	refactor: cleanup internal `TlsParameters` and `(Async)NetworkStream` config (#1082 )	2025-05-01 14:00:56 +02:00
dependabot[bot]	c91b356a96	build(deps): bump tokio from 1.44.1 to 1.44.2 (#1080 ) 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>	2025-04-08 06:57:33 +02:00
dependabot[bot]	118c1ad47f	build(deps): bump openssl from 0.10.71 to 0.10.72 (#1079 ) Bumps [openssl](https://github.com/sfackler/rust-openssl) from 0.10.71 to 0.10.72. - [Release notes](https://github.com/sfackler/rust-openssl/releases) - [Commits](https://github.com/sfackler/rust-openssl/compare/openssl-v0.10.71...openssl-v0.10.72) --- updated-dependencies: - dependency-name: openssl dependency-version: 0.10.72 dependency-type: indirect ... Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>	2025-04-06 11:49:28 +02:00
Paolo Barbolini	8bf4d3a9c1	style: fix `clippy::io_other_error` (#1078 )	2025-04-03 10:28:06 +00:00
Paolo Barbolini	1fcff673ba	fix: remove `E: Clone` bound from `AsyncFileTransport` `Clone` impl (#1075 )	2025-04-03 08:05:39 +00:00
Paolo Barbolini	8c70c0cfb4	build(deps): upgrade semver compatible dependencies (#1076 )	2025-04-03 07:54:06 +00:00
Paolo Barbolini	63d8d30088	fix: let cannot be used for global variables (#1077 )	2025-04-03 09:50:06 +02:00
Paolo Barbolini	6c0be84817	Prepare v0.11.15 (#1070 )	2025-03-10 17:26:17 +01:00
Paolo Barbolini	6059cb04d6	build(deps): upgrade email-encoding to v0.4 (#1069 )	2025-03-09 07:22:20 +00:00
Paolo Barbolini	fdf0346556	style: fix `rustdoc::broken_intra_doc_links` (#1068 )	2025-03-09 07:55:15 +01:00
Paolo Barbolini	0f9455715c	build(deps): upgrade semver compatible locked dependencies (#1067 )	2025-03-08 11:52:38 +00:00
Popax21	0b3a1ed278	feat: add controlled shutdown methods (#1045 )	2025-03-08 12:43:05 +01:00
Paolo Barbolini	76bf68268f	build(deps): bump minimum supported serde to v1.0.110 (#1064 )	2025-03-04 13:06:17 +01:00
Paolo Barbolini	99a86c0fac	build(deps): bump minimum supported rustls to v0.23.18 (#1063 )	2025-03-04 12:55:43 +01:00
Paolo Barbolini	f0de9ef02c	style: deny `unreachable_pub` lint (#1058 )	2025-02-23 10:17:17 +01:00
Paolo Barbolini	b4ddcbdcfc	build: bump MSRV to 1.74 (#1060 )	2025-02-23 10:16:57 +01:00
Paolo Barbolini	1e22bcd527	Prepare v0.11.14 (#1056 )	2025-02-23 10:06:28 +01:00
Paolo Barbolini	75716ca269	feat: make crypto and TLS certificate verify backends opt-in (#1054 )	2025-02-23 09:32:47 +01:00
Paolo Barbolini	8a6f1dab0e	deprecate: having made `AsyncNetworkStream` public (#1059 )	2025-02-22 21:22:30 +01:00
Paolo Barbolini	621853e2e3	chore(license): bump my copyright year (#1057 )	2025-02-22 20:27:07 +01:00
Paolo Barbolini	5e4cb2d1b5	fix: use the same `rustls` crypto provider everywhere (#1055 )	2025-02-22 19:14:28 +01:00
Paolo Barbolini	b4abd40698	style: fix `rustls-native-tls` warnings when `tracing` is disabled (#1053 )	2025-02-22 17:39:39 +00:00
Paolo Barbolini	2d1ccda2ef	style(clippy): ban direct use of `std::time::SystemTime::now` (#1043 )	2025-02-22 08:32:38 +00:00
Paolo Barbolini	54934e1492	build(deps): drop direct dependency on rustls-pki-types (#1051 )	2025-02-22 08:07:23 +00:00
Paolo Barbolini	cfa29743a8	refactor: replace `rustls-pemfile` with `rustls-pki-types` (#1050 )	2025-02-22 08:59:14 +01:00
Paolo Barbolini	4a4a96d805	refactor: remove artifact from `web-time` refactor (#1049 )	2025-02-22 07:44:56 +00:00
Paolo Barbolini	f0b8052a52	build(deps): upgrade nom to v8 (#1048 )	2025-02-22 08:36:56 +01:00
Paolo Barbolini	655cd8a140	style: cleanup Cargo.toml (#1047 )	2025-02-22 08:30:01 +01:00
Paolo Barbolini	dabc88a053	Prepare v0.11.13 (#1044 )	2025-02-17 11:48:42 +01:00
Paolo Barbolini	9cdefcea09	refactor: simplify handling of WASM `web-time` (#1042 )	2025-02-17 09:05:22 +00:00
Abid Omar	5748af4c98	feat: add WASM support via `web-time` (#1037 ) Support WASM environments by using web-time. This was tested on a Cloudflare worker environment.	2025-02-17 09:53:19 +01:00
André Cruz	3e9b1876d9	feat: add method to obtain TLS result (#1039 ) Some TLS toolkits export a result that can be checked afterwards even if the TLS negotation returned successfully. This can be used for example if you disabled certificate checks by default, but then want to check the outcome. Currently this is only supported on boring TLS.	2025-02-17 09:51:45 +01:00
Popax21	795bedae76	fix: synchronous pool shutdowns being arbitrarily delayed (#1041 ) Previously, the connection pool thread did not drop its upgraded `Arc` pool reference while sleeping until the next idle duration check. This causes a drop of the `SmtpTransport` to not shut down any connections until said thread wakes up again (since it still holds a reference to the pool), which can take up to 60s with default settings. In practice, this means that connections will most likely not be properly closed before the program exists, (since the `SmtpTransport` is most likely dropped when the program shuts down) which violates the SMTP specification which states that: > The sender MUST NOT intentionally close the channel until it sends a QUIT command, and it SHOULD wait until it receives the reply (even if there was an error response to a command).	2025-02-07 08:29:06 +01:00
dependabot[bot]	891dd521ab	build(deps): bump openssl from 0.10.68 to 0.10.70 (#1038 ) Bumps [openssl](https://github.com/sfackler/rust-openssl) from 0.10.68 to 0.10.70. - [Release notes](https://github.com/sfackler/rust-openssl/releases) - [Commits](https://github.com/sfackler/rust-openssl/compare/openssl-v0.10.68...openssl-v0.10.70) --- updated-dependencies: - dependency-name: openssl dependency-type: indirect ... Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>	2025-02-03 20:51:45 +01:00
Paolo Barbolini	0fb89e23ad	Prepare v0.11.12 (#1034 )	2025-02-02 14:05:41 +01:00
Paolo Barbolini	097f7d5aaa	docs: fix broken doc link (#1036 )	2025-02-02 13:49:52 +01:00
Paolo Barbolini	32e066464a	docs: improve SMTP transport `from_url` (#1032 )	2025-02-02 13:38:03 +01:00
Paolo Barbolini	55c7f57f25	docs: improve `transport::smtp` (#1031 )	2025-02-02 13:37:25 +01:00
Paolo Barbolini	3f7a57a417	docs: replace `assert!` with `?` operator for `send` examples (#1033 )	2025-02-02 13:33:34 +01:00
Paolo Barbolini	bb64baec67	style: warn on more pedantic clippy lints and fix them (#1035 )	2025-02-02 12:50:15 +01:00
Paolo Barbolini	5f13636b49	docs: document OpenSSL system dependencies (#1030 )	2025-02-01 22:14:14 +01:00
Paolo Barbolini	4513e602d6	docs: fix credentials copy-paste error (#1019 )	2024-12-25 09:05:34 +01:00
Paolo Barbolini	382e15013a	docs: document (Async)SmtpTransport (#1018 )	2024-12-25 09:05:24 +01:00
Paolo Barbolini	3ce31c5a6a	docs: add missing ContentType to email building (#1017 )	2024-12-23 22:08:08 +01:00
Paolo Barbolini	a48cf92a5b	docs: fix rustdoc warnings (#1016 )	2024-12-23 17:19:24 +01:00
Paolo Barbolini	43f6f139d2	docs: improve docs for Tls enum (#1015 )	2024-12-23 17:01:24 +01:00
Paolo Barbolini	fd1425666d	docs: warn against manually configuring port and tls configs (#1014 )	2024-12-23 16:43:39 +01:00
Paolo Barbolini	de075153b0	Prepare v0.11.11 (#1013 )	2024-12-05 20:48:10 +01:00
Paolo Barbolini	02dfc7dd4a	fix: off-by-one error reaching the min number of pooled connections (#1012 )	2024-12-05 19:19:54 +01:00
Paolo Barbolini	83ce5872d7	Fix some clippy warnings (#1009 )	2024-11-28 15:48:08 +00:00
Paolo Barbolini	272efeca74	build(deps): bump locked dependencies (#1006 )	2024-11-27 10:21:13 +01:00
Paolo Barbolini	ec6f5f3920	build: bump MSRV to 1.71 (#1008 )	2024-11-27 10:15:59 +01:00
Paolo Barbolini	b62d23bd87	build: fix -Zminimal-versions build (#1007 )	2024-11-27 10:11:49 +01:00
Paolo Barbolini	51794aa912	Prepare v0.11.10 (#1002 )	2024-10-23 23:04:45 +02:00
Paolo Barbolini	eb42651401	Use case insensitive comparisons for login challenge requests (#1000 )	2024-10-23 20:01:00 +02:00
Paolo Barbolini	99c6dc2a87	Replace `quit` with `abort` in transport connection drop code (#999 )	2024-10-23 20:00:31 +02:00