Prepare v0.11.18

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

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

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

.github/workflows/test.yml

@@ -75,8 +75,8 @@ jobs:
             rust: stable
           - name: beta
             rust: beta
-          - name: '1.71'
+          - name: '1.74'
-            rust: '1.71'
+            rust: '1.74'
 
     steps:
       - name: Checkout

CHANGELOG.md

@@ -1,3 +1,99 @@
+<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)
 

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 = "0.11.14"
+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 = "1.71"
+rust-version = "1.74"
 
 [badges]
 is-it-maintained-issue-resolution = { repository = "lettre/lettre" }
@@ -32,25 +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", features = ["derive"], optional = true }
+serde = { version = "1.0.110", features = ["derive"], optional = true }
 serde_json = { version = "1", optional = true }
 
 # smtp-transport
 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 = "0.2.9", optional = true } # feature
-rustls = { version = "0.23.5", default-features = false, features = ["logging", "std", "tls12"], optional = true }
+rustls = { version = "0.23.18", default-features = false, features = ["logging", "std", "tls12"], optional = true }
+rustls-platform-verifier = { version = "0.6.0", optional = true }
 rustls-native-certs = { version = "0.8", optional = true }
-webpki-roots = { version = "0.26", optional = true }
+webpki-roots = { version = "1.0.0", optional = true }
 boring = { version = "4", optional = true }
 
 # async
@@ -73,6 +74,7 @@ sha2 = { version = "0.10", features = ["oid"], optional = true }
 rsa = { version = "0.9", optional = true }
 ed25519-dalek = { version = "2", optional = true }
 
+[target.'cfg(target_arch = "wasm32")'.dependencies]
 ## web-time for wasm support
 web-time = { version = "1.1.0", optional = true }
 

README.md

@@ -28,8 +28,8 @@
 </div>
 
 <div align="center">
-  <a href="https://deps.rs/crate/lettre/0.11.14">
+  <a href="https://deps.rs/crate/lettre/0.11.18">
-    <img src="https://deps.rs/crate/lettre/0.11.14/status.svg"
+    <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 1.71, 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 1.71 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())
+        .from(Mailbox::new("NoBody".to_owned(), "nobody@domain.tld".parse().unwrap()))
-        .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
+        .reply_to(Mailbox::new("Yuin".to_owned(), "yuin@domain.tld".parse().unwrap()))
-        .to("Hei <hei@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!"))

src/address/envelope.rs

@@ -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;
 

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 {
+pub(crate) trait SpawnHandle: Debug + Send + Sync + 'static + private::Sealed {
-    async fn shutdown(self);
+    async fn shutdown(&self);
 }
 
 /// Async [`Executor`] using `tokio` `1.x`
@@ -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")]
@@ -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<()> {
+impl SpawnHandle for futures_util::future::AbortHandle {
-    async fn shutdown(self) {
+    async fn shutdown(&self) {
-        self.cancel().await;
+        self.abort();
     }
 }
 
@@ -291,5 +294,5 @@ mod private {
     impl Sealed for tokio1_crate::task::JoinHandle<()> {}
 
     #[cfg(all(feature = "smtp-transport", feature = "async-std1"))]
-    impl Sealed for async_std::task::JoinHandle<()> {}
+    impl Sealed for futures_util::future::AbortHandle {}
 }

src/lib.rs

@@ -6,7 +6,7 @@
 //! * Secure defaults
 //! * Async support
 //!
-//! Lettre requires Rust 1.71 or newer.
+//! Lettre requires Rust 1.74 or newer.
 //!
 //! ## Features
 //!
@@ -93,17 +93,20 @@
 //! When the `rustls` feature is enabled, one of the following verification backends
 //! MUST also be enabled.
 //!
-//! * **rustls-native-certs**: verify TLS certificates using the platform's native certificate store (see [`rustls-native-certs`])
+//! * **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`])
 //!
-//! For the `rustls-native-certs` backend to work correctly, the following packages
+//! The following packages will need to be installed in order for the build
-//! will need to be installed in order for the build stage and the compiled program
+//! stage and the compiled program to run properly.
-//! to run properly.
 //!
-//! | Distro       | Build-time packages        | Runtime packages             |
+//! | Verification backend       | Distro       | Build-time packages        | Runtime packages             |
-//! | ------------ | -------------------------- | ---------------------------- |
+//! | ---------------------      | ------------ | -------------------------- | ---------------------------- |
-//! | Debian       | none                       | `ca-certificates`            |
+//! | `rustls-platform-verifier` | Debian       | none                       | `ca-certificates`            |
-//! | Alpine Linux | 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
 //!
@@ -151,6 +154,7 @@
 //! [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
@@ -158,11 +162,12 @@
 //! [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/0.11.14")]
+#![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,
@@ -207,12 +212,13 @@ mod compiletime_checks {
 
     #[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-native-certs` or the `webpki-roots` feature to
+        "feature `rustls` also requires either the `rustls-platform-verifier`, the `rustls-native-certs`
-    be enabled"
+    or the `webpki-roots` feature to be enabled"
     );
 
     #[cfg(all(feature = "native-tls", feature = "boring-tls"))]

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"
+            )
+        );
+    }
 }

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())
 }

src/time.rs

@@ -1,6 +1,6 @@
 use std::time::SystemTime;
 
-#[cfg(feature = "web")]
+#[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
@@ -18,7 +18,7 @@ pub(crate) fn now() -> SystemTime {
     to_std_systemtime(web_time::SystemTime::now())
 }
 
-#[cfg(not(feature = "web"))]
+#[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)]

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)
     }

src/transport/file/mod.rs

@@ -173,7 +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"))]
@@ -199,6 +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()),
@@ -211,6 +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;
 
@@ -249,6 +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),
@@ -260,6 +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)?;
@@ -272,6 +276,16 @@ where
     }
 }
 
+#[cfg(any(feature = "async-std1", feature = "tokio1"))]
+impl<E: Executor> Clone for AsyncFileTransport<E> {
+    fn clone(&self) -> Self {
+        Self {
+            inner: self.inner.clone(),
+            marker_: PhantomData,
+        }
+    }
+}
+
 impl Transport for FileTransport {
     type Ok = Id;
     type Error = Error;

src/transport/mod.rs

@@ -140,6 +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
@@ -166,4 +170,8 @@ pub trait AsyncTransport {
     }
 
     async fn send_raw(&self, envelope: &Envelope, email: &[u8]) -> Result<Self::Ok, Self::Error>;
+
+    /// Shuts down the transport. Future calls to [`Self::send`] and
+    /// [`Self::send_raw`] might fail.
+    async fn shutdown(&self) {}
 }

src/transport/smtp/async_transport.rs

@@ -79,6 +79,11 @@ impl AsyncTransport for AsyncSmtpTransport<Tokio1Executor> {
 
         Ok(result)
     }
+
+    async fn shutdown(&self) {
+        #[cfg(feature = "pool")]
+        self.inner.shutdown().await;
+    }
 }
 
 #[cfg(feature = "async-std1")]
@@ -97,6 +102,11 @@ impl AsyncTransport for AsyncSmtpTransport<AsyncStd1Executor> {
 
         Ok(result)
     }
+
+    async fn shutdown(&self) {
+        #[cfg(feature = "pool")]
+        self.inner.shutdown().await;
+    }
 }
 
 impl<E> AsyncSmtpTransport<E>
@@ -224,7 +234,7 @@ where
     /// a proper URL encoder, like the following cargo script:
     ///
     /// ```rust
-    /// # let _ = r#"
+    /// # const TOML: &str = r#"
     /// #!/usr/bin/env cargo
     ///
     /// //! ```cargo
@@ -460,7 +470,7 @@ impl AsyncSmtpTransportBuilder {
 }
 
 /// Build client
-pub struct AsyncSmtpClient<E> {
+pub(super) struct AsyncSmtpClient<E> {
     info: SmtpInfo,
     marker_: PhantomData<E>,
 }
@@ -472,7 +482,7 @@ where
     /// Creates a new connection directly usable to send emails
     ///
     /// Handles encryption and authentication
-    pub async fn connection(&self) -> Result<AsyncSmtpConnection, Error> {
+    pub(super) async fn connection(&self) -> Result<AsyncSmtpConnection, Error> {
         let mut conn = E::connect(
             &self.info.server,
             self.info.port,

src/transport/smtp/client/async_connection.rs

@@ -54,6 +54,7 @@ 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,
@@ -94,6 +95,7 @@ impl AsyncSmtpConnection {
     /// # }
     /// ```
     #[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>,
@@ -112,6 +114,7 @@ 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>,
@@ -376,6 +379,10 @@ impl AsyncSmtpConnection {
 
     /// The X509 certificate of the server (DER encoded)
     #[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()
     }
@@ -392,12 +399,14 @@ impl AsyncSmtpConnection {
     /// as the TLSA records match the leaf or issuer certificates.
     /// It cannot be called on non Boring TLS streams.
     #[cfg(feature = "boring-tls")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "boring-tls")))]
     pub fn tls_verify_result(&self) -> Result<(), Error> {
         self.stream.get_ref().tls_verify_result()
     }
 
     /// All the X509 certificates of the chain (DER encoded)
     #[cfg(any(feature = "rustls", feature = "boring-tls"))]
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "rustls", feature = "boring-tls"))))]
     pub fn certificate_chain(&self) -> Result<Vec<Vec<u8>>, Error> {
         self.stream.get_ref().certificate_chain()
     }

src/transport/smtp/client/async_net.rs

@@ -9,11 +9,11 @@ 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")]
-use futures_rustls::client::TlsStream as AsyncStd1RustlsTlsStream;
+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")]
@@ -28,7 +28,7 @@ use tokio1_crate::net::{
 #[cfg(feature = "tokio1-native-tls")]
 use tokio1_native_tls_crate::TlsStream as Tokio1TlsStream;
 #[cfg(feature = "tokio1-rustls")]
-use tokio1_rustls::client::TlsStream as Tokio1RustlsTlsStream;
+use tokio1_rustls::client::TlsStream as Tokio1RustlsStream;
 
 #[cfg(any(
     feature = "tokio1-native-tls",
@@ -79,7 +79,7 @@ enum InnerAsyncNetworkStream {
     Tokio1NativeTls(Tokio1TlsStream<Box<dyn AsyncTokioStream>>),
     /// Encrypted Tokio 1.x TCP stream
     #[cfg(feature = "tokio1-rustls")]
-    Tokio1RustlsTls(Tokio1RustlsTlsStream<Box<dyn AsyncTokioStream>>),
+    Tokio1Rustls(Tokio1RustlsStream<Box<dyn AsyncTokioStream>>),
     /// Encrypted Tokio 1.x TCP stream
     #[cfg(feature = "tokio1-boring-tls")]
     Tokio1BoringTls(Tokio1SslStream<Box<dyn AsyncTokioStream>>),
@@ -88,7 +88,7 @@ enum InnerAsyncNetworkStream {
     AsyncStd1Tcp(AsyncStd1TcpStream),
     /// Encrypted Tokio 1.x TCP stream
     #[cfg(feature = "async-std1-rustls")]
-    AsyncStd1RustlsTls(AsyncStd1RustlsTlsStream<AsyncStd1TcpStream>),
+    AsyncStd1Rustls(AsyncStd1RustlsStream<AsyncStd1TcpStream>),
     /// Can't be built
     None,
 }
@@ -113,17 +113,16 @@ impl AsyncNetworkStream {
                 s.get_ref().get_ref().get_ref().peer_addr()
             }
             #[cfg(feature = "tokio1-rustls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => s.get_ref().0.peer_addr(),
+            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")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => s.get_ref().0.peer_addr(),
+            InnerAsyncNetworkStream::AsyncStd1Rustls(s) => s.get_ref().0.peer_addr(),
             InnerAsyncNetworkStream::None => {
                 debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
-                Err(IoError::new(
+                Err(IoError::other(
-                    ErrorKind::Other,
                     "InnerAsyncNetworkStream::None must never be built",
                 ))
             }
@@ -131,11 +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>,
@@ -202,6 +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>,
@@ -321,7 +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");
 
@@ -338,7 +340,7 @@ impl AsyncNetworkStream {
                 };
             }
             #[cfg(feature = "rustls")]
-            InnerTlsParameters::RustlsTls(config) => {
+            InnerTlsParameters::Rustls { config } => {
                 #[cfg(not(feature = "tokio1-rustls"))]
                 panic!("built without the tokio1-rustls feature");
 
@@ -354,18 +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
@@ -386,11 +391,11 @@ 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")]
-            InnerTlsParameters::RustlsTls(config) => {
+            InnerTlsParameters::Rustls { config } => {
                 #[cfg(not(feature = "async-std1-rustls"))]
                 panic!("built without the async-std1-rustls feature");
 
@@ -406,11 +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.");
             }
         }
@@ -423,18 +428,19 @@ impl AsyncNetworkStream {
             #[cfg(feature = "tokio1-native-tls")]
             InnerAsyncNetworkStream::Tokio1NativeTls(_) => true,
             #[cfg(feature = "tokio1-rustls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(_) => true,
+            InnerAsyncNetworkStream::Tokio1Rustls(_) => true,
             #[cfg(feature = "tokio1-boring-tls")]
             InnerAsyncNetworkStream::Tokio1BoringTls(_) => true,
             #[cfg(feature = "async-std1")]
             InnerAsyncNetworkStream::AsyncStd1Tcp(_) => false,
             #[cfg(feature = "async-std1-rustls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(_) => true,
+            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")]
@@ -444,7 +450,7 @@ impl AsyncNetworkStream {
             #[cfg(feature = "tokio1-native-tls")]
             InnerAsyncNetworkStream::Tokio1NativeTls(_) => panic!("Unsupported"),
             #[cfg(feature = "tokio1-rustls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(_) => panic!("Unsupported"),
+            InnerAsyncNetworkStream::Tokio1Rustls(_) => panic!("Unsupported"),
             #[cfg(feature = "tokio1-boring-tls")]
             InnerAsyncNetworkStream::Tokio1BoringTls(stream) => {
                 stream.ssl().verify_result().map_err(error::tls)
@@ -454,10 +460,11 @@ impl AsyncNetworkStream {
                 Err(error::client("Connection is not encrypted"))
             }
             #[cfg(feature = "async-std1-rustls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(_) => panic!("Unsupported"),
+            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")]
@@ -467,7 +474,7 @@ impl AsyncNetworkStream {
             #[cfg(feature = "tokio1-native-tls")]
             InnerAsyncNetworkStream::Tokio1NativeTls(_) => panic!("Unsupported"),
             #[cfg(feature = "tokio1-rustls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(stream) => Ok(stream
+            InnerAsyncNetworkStream::Tokio1Rustls(stream) => Ok(stream
                 .get_ref()
                 .1
                 .peer_certificates()
@@ -488,7 +495,7 @@ impl AsyncNetworkStream {
                 Err(error::client("Connection is not encrypted"))
             }
             #[cfg(feature = "async-std1-rustls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(stream) => Ok(stream
+            InnerAsyncNetworkStream::AsyncStd1Rustls(stream) => Ok(stream
                 .get_ref()
                 .1
                 .peer_certificates()
@@ -515,7 +522,7 @@ impl AsyncNetworkStream {
                 .to_der()
                 .map_err(error::tls)?),
             #[cfg(feature = "tokio1-rustls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(stream) => Ok(stream
+            InnerAsyncNetworkStream::Tokio1Rustls(stream) => Ok(stream
                 .get_ref()
                 .1
                 .peer_certificates()
@@ -535,7 +542,7 @@ impl AsyncNetworkStream {
                 Err(error::client("Connection is not encrypted"))
             }
             #[cfg(feature = "async-std1-rustls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(stream) => Ok(stream
+            InnerAsyncNetworkStream::AsyncStd1Rustls(stream) => Ok(stream
                 .get_ref()
                 .1
                 .peer_certificates()
@@ -575,7 +582,7 @@ impl FuturesAsyncRead for AsyncNetworkStream {
                 }
             }
             #[cfg(feature = "tokio1-rustls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => {
+            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())),
@@ -595,7 +602,7 @@ impl FuturesAsyncRead for AsyncNetworkStream {
             #[cfg(feature = "async-std1")]
             InnerAsyncNetworkStream::AsyncStd1Tcp(s) => Pin::new(s).poll_read(cx, buf),
             #[cfg(feature = "async-std1-rustls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => Pin::new(s).poll_read(cx, buf),
+            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))
@@ -617,13 +624,13 @@ impl FuturesAsyncWrite for AsyncNetworkStream {
             #[cfg(feature = "tokio1-native-tls")]
             InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_write(cx, buf),
             #[cfg(feature = "tokio1-rustls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => Pin::new(s).poll_write(cx, buf),
+            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")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => Pin::new(s).poll_write(cx, buf),
+            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))
@@ -638,13 +645,13 @@ impl FuturesAsyncWrite for AsyncNetworkStream {
             #[cfg(feature = "tokio1-native-tls")]
             InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_flush(cx),
             #[cfg(feature = "tokio1-rustls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => Pin::new(s).poll_flush(cx),
+            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")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::AsyncStd1Rustls(s) => Pin::new(s).poll_flush(cx),
             InnerAsyncNetworkStream::None => {
                 debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
                 Poll::Ready(Ok(()))
@@ -659,13 +666,13 @@ impl FuturesAsyncWrite for AsyncNetworkStream {
             #[cfg(feature = "tokio1-native-tls")]
             InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_shutdown(cx),
             #[cfg(feature = "tokio1-rustls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => Pin::new(s).poll_shutdown(cx),
+            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")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => Pin::new(s).poll_close(cx),
+            InnerAsyncNetworkStream::AsyncStd1Rustls(s) => Pin::new(s).poll_close(cx),
             InnerAsyncNetworkStream::None => {
                 debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
                 Poll::Ready(Ok(()))

src/transport/smtp/client/connection.rs

@@ -300,6 +300,10 @@ impl SmtpConnection {
 
     /// The X509 certificate of the server (DER encoded)
     #[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()
     }
@@ -316,12 +320,14 @@ impl SmtpConnection {
     /// as the TLSA records match the leaf or issuer certificates.
     /// It cannot be called on non Boring TLS streams.
     #[cfg(feature = "boring-tls")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "boring-tls")))]
     pub fn tls_verify_result(&self) -> Result<(), Error> {
         self.stream.get_ref().tls_verify_result()
     }
 
     /// All the X509 certificates of the chain (DER encoded)
     #[cfg(any(feature = "rustls", feature = "boring-tls"))]
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "rustls", feature = "boring-tls"))))]
     pub fn certificate_chain(&self) -> Result<Vec<Vec<u8>>, Error> {
         self.stream.get_ref().certificate_chain()
     }

src/transport/smtp/client/mod.rs

@@ -58,7 +58,7 @@ struct ClientCodec {
 
 impl ClientCodec {
     /// Creates a new client codec
-    pub fn new() -> Self {
+    pub(crate) fn new() -> Self {
         Self {
             status: CodecStatus::StartOfNewLine,
         }

src/transport/smtp/client/net.rs

@@ -37,7 +37,7 @@ enum InnerNetworkStream {
     NativeTls(TlsStream<TcpStream>),
     /// Encrypted TCP stream
     #[cfg(feature = "rustls")]
-    RustlsTls(StreamOwned<ClientConnection, TcpStream>),
+    Rustls(StreamOwned<ClientConnection, TcpStream>),
     #[cfg(feature = "boring-tls")]
     BoringTls(SslStream<TcpStream>),
     /// Can't be built
@@ -60,7 +60,7 @@ impl NetworkStream {
             #[cfg(feature = "native-tls")]
             InnerNetworkStream::NativeTls(s) => s.get_ref().peer_addr(),
             #[cfg(feature = "rustls")]
-            InnerNetworkStream::RustlsTls(s) => s.get_ref().peer_addr(),
+            InnerNetworkStream::Rustls(s) => s.get_ref().peer_addr(),
             #[cfg(feature = "boring-tls")]
             InnerNetworkStream::BoringTls(s) => s.get_ref().peer_addr(),
             InnerNetworkStream::None => {
@@ -80,7 +80,7 @@ impl NetworkStream {
             #[cfg(feature = "native-tls")]
             InnerNetworkStream::NativeTls(s) => s.get_ref().shutdown(how),
             #[cfg(feature = "rustls")]
-            InnerNetworkStream::RustlsTls(s) => s.get_ref().shutdown(how),
+            InnerNetworkStream::Rustls(s) => s.get_ref().shutdown(how),
             #[cfg(feature = "boring-tls")]
             InnerNetworkStream::BoringTls(s) => s.get_ref().shutdown(how),
             InnerNetworkStream::None => {
@@ -174,27 +174,30 @@ impl NetworkStream {
     ) -> 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")]
-            InnerTlsParameters::RustlsTls(connector) => {
+            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)
@@ -208,7 +211,7 @@ impl NetworkStream {
             #[cfg(feature = "native-tls")]
             InnerNetworkStream::NativeTls(_) => true,
             #[cfg(feature = "rustls")]
-            InnerNetworkStream::RustlsTls(_) => true,
+            InnerNetworkStream::Rustls(_) => true,
             #[cfg(feature = "boring-tls")]
             InnerNetworkStream::BoringTls(_) => true,
             InnerNetworkStream::None => {
@@ -219,13 +222,14 @@ impl NetworkStream {
     }
 
     #[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::RustlsTls(_) => panic!("Unsupported"),
+            InnerNetworkStream::Rustls(_) => panic!("Unsupported"),
             #[cfg(feature = "boring-tls")]
             InnerNetworkStream::BoringTls(stream) => {
                 stream.ssl().verify_result().map_err(error::tls)
@@ -235,13 +239,14 @@ impl NetworkStream {
     }
 
     #[cfg(any(feature = "rustls", feature = "boring-tls"))]
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "rustls", feature = "boring-tls"))))]
     pub fn certificate_chain(&self) -> Result<Vec<Vec<u8>>, Error> {
         match &self.inner {
             InnerNetworkStream::Tcp(_) => Err(error::client("Connection is not encrypted")),
             #[cfg(feature = "native-tls")]
             InnerNetworkStream::NativeTls(_) => panic!("Unsupported"),
             #[cfg(feature = "rustls")]
-            InnerNetworkStream::RustlsTls(stream) => Ok(stream
+            InnerNetworkStream::Rustls(stream) => Ok(stream
                 .conn
                 .peer_certificates()
                 .unwrap()
@@ -261,6 +266,10 @@ impl NetworkStream {
     }
 
     #[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")),
@@ -272,7 +281,7 @@ impl NetworkStream {
                 .to_der()
                 .map_err(error::tls)?),
             #[cfg(feature = "rustls")]
-            InnerNetworkStream::RustlsTls(stream) => Ok(stream
+            InnerNetworkStream::Rustls(stream) => Ok(stream
                 .conn
                 .peer_certificates()
                 .unwrap()
@@ -296,7 +305,7 @@ impl NetworkStream {
             #[cfg(feature = "native-tls")]
             InnerNetworkStream::NativeTls(stream) => stream.get_ref().set_read_timeout(duration),
             #[cfg(feature = "rustls")]
-            InnerNetworkStream::RustlsTls(stream) => stream.get_ref().set_read_timeout(duration),
+            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 => {
@@ -314,7 +323,7 @@ impl NetworkStream {
             #[cfg(feature = "native-tls")]
             InnerNetworkStream::NativeTls(stream) => stream.get_ref().set_write_timeout(duration),
             #[cfg(feature = "rustls")]
-            InnerNetworkStream::RustlsTls(stream) => stream.get_ref().set_write_timeout(duration),
+            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 => {
@@ -332,7 +341,7 @@ impl Read for NetworkStream {
             #[cfg(feature = "native-tls")]
             InnerNetworkStream::NativeTls(s) => s.read(buf),
             #[cfg(feature = "rustls")]
-            InnerNetworkStream::RustlsTls(s) => s.read(buf),
+            InnerNetworkStream::Rustls(s) => s.read(buf),
             #[cfg(feature = "boring-tls")]
             InnerNetworkStream::BoringTls(s) => s.read(buf),
             InnerNetworkStream::None => {
@@ -350,7 +359,7 @@ impl Write for NetworkStream {
             #[cfg(feature = "native-tls")]
             InnerNetworkStream::NativeTls(s) => s.write(buf),
             #[cfg(feature = "rustls")]
-            InnerNetworkStream::RustlsTls(s) => s.write(buf),
+            InnerNetworkStream::Rustls(s) => s.write(buf),
             #[cfg(feature = "boring-tls")]
             InnerNetworkStream::BoringTls(s) => s.write(buf),
             InnerNetworkStream::None => {
@@ -366,7 +375,7 @@ impl Write for NetworkStream {
             #[cfg(feature = "native-tls")]
             InnerNetworkStream::NativeTls(s) => s.flush(),
             #[cfg(feature = "rustls")]
-            InnerNetworkStream::RustlsTls(s) => s.flush(),
+            InnerNetworkStream::Rustls(s) => s.flush(),
             #[cfg(feature = "boring-tls")]
             InnerNetworkStream::BoringTls(s) => s.flush(),
             InnerNetworkStream::None => {

src/transport/smtp/client/tls.rs

@@ -65,6 +65,16 @@ pub enum TlsVersion {
 /// 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 (plaintext) connection only.
     ///
@@ -138,14 +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
+    /// For rustls, this will use the system certificate verifier if the `rustls-platform-verifier`
-    /// enabled, or will fall back to `webpki-roots`.
+    /// 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]
@@ -161,16 +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,
@@ -221,6 +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
@@ -244,6 +285,10 @@ impl TlsParametersBuilder {
     ///
     /// Defaults to [`Tlsv12`][TlsVersion::Tlsv12].
     #[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
@@ -328,10 +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,
         })
     }
 
@@ -389,9 +432,11 @@ 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,
         })
     }
 
@@ -419,7 +464,10 @@ impl TlsParametersBuilder {
         // Build TLS config
         let mut root_cert_store = RootCertStore::empty();
 
-        #[cfg(feature = "rustls-native-certs")]
+        #[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();
@@ -439,11 +487,26 @@ impl TlsParametersBuilder {
             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")]
+                #[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-native-certs"), feature = "webpki-roots"))]
+
+                #[cfg(all(
+                    not(feature = "rustls-platform-verifier"),
+                    not(feature = "rustls-native-certs"),
+                    feature = "webpki-roots"
+                ))]
                 load_webpki_roots(&mut root_cert_store);
             }
             #[cfg(all(feature = "rustls", feature = "webpki-roots"))]
@@ -454,11 +517,17 @@ 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,
@@ -468,7 +537,23 @@ impl TlsParametersBuilder {
             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 {
@@ -480,23 +565,26 @@ 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),
+    NativeTls { connector: TlsConnector },
     #[cfg(feature = "rustls")]
-    RustlsTls(Arc<ClientConfig>),
+    Rustls { config: Arc<ClientConfig> },
     #[cfg(feature = "boring-tls")]
-    BoringTls(SslConnector),
+    BoringTls {
+        connector: SslConnector,
+        accept_invalid_hostnames: bool,
+    },
 }
 
 impl TlsParameters {
@@ -545,6 +633,16 @@ 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,
@@ -608,6 +706,16 @@ 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,

src/transport/smtp/connection_url.rs

@@ -13,6 +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;
@@ -24,6 +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)
     }
@@ -47,6 +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)
     }

src/transport/smtp/error.rs

@@ -77,6 +77,11 @@ impl Error {
         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 {
@@ -111,6 +116,8 @@ pub(crate) enum Kind {
     )]
     #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
     Tls,
+    /// Transport shutdown error
+    TransportShutdown,
 }
 
 impl fmt::Debug for Error {
@@ -136,6 +143,7 @@ impl fmt::Display for Error {
             Kind::Connection => f.write_str("Connection error")?,
             #[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})")?;
             }
@@ -189,3 +197,7 @@ pub(crate) fn connection<E: Into<BoxError>>(e: E) -> Error {
 pub(crate) fn tls<E: Into<BoxError>>(e: E) -> Error {
     Error::new(Kind::Tls, Some(e))
 }
+
+pub(crate) fn transport_shutdown() -> Error {
+    Error::new::<BoxError>(Kind::TransportShutdown, None)
+}

src/transport/smtp/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()
@@ -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")]
@@ -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;
+            let mut connections_guard = self.connections.lock().await;
-            if connections.len() >= self.config.max_size as usize {
+
-                drop(connections);
+            if let Some(connections) = connections_guard.as_mut() {
-                conn.abort().await;
+                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);
+                // The pool has already been shut down
-                connections.push(conn);
+                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(ParkedConnection::unpark)).await;
+            if let Some(connections) = connections {
+                abort_concurrent(connections.into_iter().map(ParkedConnection::unpark)).await;
+            }
         });
     }
 }

src/transport/smtp/pool/mod.rs

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

src/transport/smtp/pool/sync_impl.rs

@@ -1,8 +1,7 @@
 use std::{
     fmt::{self, Debug},
-    mem,
     ops::{Deref, DerefMut},
-    sync::{Arc, Mutex, TryLockError},
+    sync::{mpsc, Arc, Mutex, TryLockError},
     thread,
     time::{Duration, Instant},
 };
@@ -11,11 +10,12 @@ use super::{
     super::{client::SmtpConnection, Error},
     PoolConfig,
 };
-use crate::transport::smtp::transport::SmtpClient;
+use crate::transport::smtp::{error, transport::SmtpClient};
 
-pub struct Pool {
+pub(crate) struct Pool {
     config: PoolConfig,
-    connections: Mutex<Vec<ParkedConnection>>,
+    connections: Mutex<Option<Vec<ParkedConnection>>>,
+    thread_terminator: mpsc::SyncSender<()>,
     client: SmtpClient,
 }
 
@@ -24,16 +24,19 @@ struct ParkedConnection {
     since: Instant,
 }
 
-pub struct PooledConnection {
+pub(crate) struct PooledConnection {
     conn: Option<SmtpConnection>,
     pool: Arc<Pool>,
 }
 
 impl Pool {
-    pub fn new(config: PoolConfig, client: SmtpClient) -> Arc<Self> {
+    pub(crate) fn new(config: PoolConfig, client: SmtpClient) -> Arc<Self> {
+        let (thread_tx, thread_rx) = mpsc::sync_channel(1);
+
         let pool = Arc::new(Self {
             config,
-            connections: Mutex::new(Vec::new()),
+            connections: Mutex::new(Some(Vec::new())),
+            thread_terminator: thread_tx,
             client,
         });
 
@@ -54,6 +57,10 @@ impl Pool {
                         #[allow(clippy::needless_collect)]
                         let (count, dropped) = {
                             let mut connections = pool.connections.lock().unwrap();
+                            let Some(connections) = connections.as_mut() else {
+                                // The transport was shut down
+                                return;
+                            };
 
                             let to_drop = connections
                                 .iter()
@@ -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")]
@@ -110,7 +122,14 @@ impl Pool {
                         }
 
                         drop(pool);
-                        thread::sleep(idle_timeout);
+
+                        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");
@@ -119,10 +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()
             };
 
@@ -166,13 +200,20 @@ impl Pool {
             #[cfg(feature = "tracing")]
             tracing::debug!("recycling connection");
 
-            let mut connections = self.connections.lock().unwrap();
+            let mut connections_guard = self.connections.lock().unwrap();
-            if connections.len() >= self.config.max_size as usize {
+
-                drop(connections);
+            if let Some(connections) = connections_guard.as_mut() {
-                conn.abort();
+                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);
+                // The pool has already been shut down
-                connections.push(conn);
+                drop(connections_guard);
+                conn.abort();
             }
         }
     }
@@ -185,7 +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(),
@@ -201,10 +248,11 @@ impl Drop for Pool {
         #[cfg(feature = "tracing")]
         tracing::debug!("dropping Pool");
 
-        let connections = mem::take(&mut *self.connections.get_mut().unwrap());
+        if let Some(connections) = self.connections.get_mut().unwrap().take() {
-        for conn in connections {
+            for conn in connections {
-            let mut conn = conn.unpark();
+                let mut conn = conn.unpark();
-            conn.abort();
+                conn.abort();
+            }
         }
     }
 }

src/transport/smtp/transport.rs

@@ -60,6 +60,11 @@ impl Transport for SmtpTransport {
 
         Ok(result)
     }
+
+    fn shutdown(&self) {
+        #[cfg(feature = "pool")]
+        self.inner.shutdown();
+    }
 }
 
 impl Debug for SmtpTransport {
@@ -172,7 +177,7 @@ impl SmtpTransport {
     /// a proper URL encoder, like the following cargo script:
     ///
     /// ```rust
-    /// # let _ = r#"
+    /// # const TOML: &str = r#"
     /// #!/usr/bin/env cargo
     ///
     /// //! ```cargo
@@ -369,7 +374,7 @@ impl SmtpTransportBuilder {
 
 /// Build client
 #[derive(Debug, Clone)]
-pub struct SmtpClient {
+pub(super) struct SmtpClient {
     info: SmtpInfo,
 }
 
@@ -377,7 +382,7 @@ 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", feature = "boring-tls"))]

src/transport/smtp/util.rs

@@ -4,7 +4,7 @@ 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 Display for XText<'_> {
     fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {

src/transport/stub/mod.rs

@@ -43,13 +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;
@@ -72,7 +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
@@ -81,7 +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 {
@@ -89,7 +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![])),
         }
     }
 
@@ -97,7 +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![])),
         }
     }
 
@@ -105,7 +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![])),
         }
     }
 
@@ -124,7 +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![])),
         }
     }
 
@@ -132,7 +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![])),
         }
     }
 
@@ -140,14 +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()
     }
 }
 
@@ -173,7 +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
     }