Improve SMTP error handling

2024-10-09 22:14:27 +02:00
40 changed files with 744 additions and 1111 deletions
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -75,8 +75,8 @@ jobs:
            rust: stable
          - name: beta
            rust: beta
-          - name: '1.71'
-            rust: '1.71'
+          - name: '1.70'
+            rust: '1.70'

    steps:
      - name: Checkout
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,82 +1,3 @@
-<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)

@@ -587,6 +508,6 @@ 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 = "0.11.13"
+version = "0.11.9"
 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 = "1.70"

 [badges]
 is-it-maintained-issue-resolution = { repository = "lettre/lettre" }
@@ -44,7 +44,7 @@ url = { version = "2.4", optional = true }
 percent-encoding = { version = "2.3", optional = true }

 ## tls
-native-tls = { version = "0.2.9", optional = true } # feature
+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 }
 rustls-native-certs = { version = "0.8", optional = true }
@@ -75,9 +75,6 @@ ed25519-dalek = { version = "2", optional = true }
 # email formats
 email_address = { version = "0.2.1", default-features = false }

-# webtime for wasm support
-web-time = { version = "1.1.0", optional = true }
-
 [dev-dependencies]
 pretty_assertions = "1"
 criterion = "0.5"
@@ -125,9 +122,6 @@ 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/README.md
+++ b/README.md
@@ -28,8 +28,8 @@
 </div>

 <div align="center">
-  <a href="https://deps.rs/crate/lettre/0.11.13">
-    <img src="https://deps.rs/crate/lettre/0.11.13/status.svg"
+  <a href="https://deps.rs/crate/lettre/0.11.9">
+    <img src="https://deps.rs/crate/lettre/0.11.9/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 1.70, but this could change at any time either from
 one of our dependencies bumping their MSRV or by a new patch release of lettre.

 ## Example

-This library requires Rust 1.71 or newer.
+This library requires Rust 1.70 or newer.
 To use this library, add the following to your `Cargo.toml`:

 ```toml
@@ -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::header::ContentType, Message, SmtpTransport, Transport};
+use lettre::{Message, SmtpTransport, Transport};

 fn bench_simple_send(c: &mut Criterion) {
    let sender = SmtpTransport::builder_dangerous("127.0.0.1")
@@ -13,7 +13,6 @@ 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));
@@ -33,7 +32,6 @@ 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/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>;
--- a/src/address/serde.rs
+++ b/src/address/serde.rs
@@ -36,7 +36,7 @@ impl<'de> Deserialize<'de> for Address {
            {
                struct FieldVisitor;

-                impl Visitor<'_> for FieldVisitor {
+                impl<'de> Visitor<'de> for FieldVisitor {
                    type Value = Field;

                    fn expecting(&self, formatter: &mut Formatter<'_>) -> FmtResult {
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -6,7 +6,7 @@
 //! * Secure defaults
 //! * Async support
 //!
-//! Lettre requires Rust 1.71 or newer.
+//! Lettre requires Rust 1.70 or newer.
 //!
 //! ## Features
 //!
@@ -34,25 +34,13 @@
 //!
 //! _Secure SMTP connections using TLS from the `native-tls` crate_
 //!
-//! Uses schannel on Windows, Security-Framework on macOS, and OpenSSL
-//! on all other platforms.
+//! Uses schannel on Windows, Security-Framework on macOS, and OpenSSL on Linux.
 //!
 //! * **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_
@@ -107,7 +95,6 @@
 //! * **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
@@ -122,7 +109,7 @@
 //! [mime 0.3]: https://docs.rs/mime/0.3
 //! [DKIM]: https://datatracker.ietf.org/doc/html/rfc6376

-#![doc(html_root_url = "https://docs.rs/crate/lettre/0.11.13")]
+#![doc(html_root_url = "https://docs.rs/crate/lettre/0.11.9")]
 #![doc(html_favicon_url = "https://lettre.rs/favicon.ico")]
 #![doc(html_logo_url = "https://avatars0.githubusercontent.com/u/15113230?v=4")]
 #![forbid(unsafe_code)]
@@ -150,14 +137,7 @@
    clippy::wildcard_imports,
    clippy::str_to_string,
    clippy::empty_structs_with_brackets,
-    clippy::zero_sized_map_values,
-    clippy::manual_let_else,
-    clippy::semicolon_if_nothing_returned,
-    clippy::unnecessary_wraps,
-    clippy::doc_markdown,
-    clippy::explicit_iter_loop,
-    clippy::redundant_closure_for_method_calls,
-    // Rust 1.86: clippy::unnecessary_semicolon,
+    clippy::zero_sized_map_values
 )]
 #![cfg_attr(docsrs, feature(doc_cfg))]

@@ -219,7 +199,6 @@ mod executor;
 #[cfg(feature = "builder")]
 #[cfg_attr(docsrs, doc(cfg(feature = "builder")))]
 pub mod message;
-mod time;
 pub mod transport;

 use std::error::Error as StdError;
--- a/src/message/dkim.rs
+++ b/src/message/dkim.rs
@@ -69,7 +69,7 @@ impl Display for DkimSigningAlgorithm {
    }
 }

-/// Describe [`DkimSigningKey`] key error
+/// Describe DkimSigning 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,
@@ -344,12 +344,10 @@ 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) {
-    #[cfg(feature = "web")]
-    dkim_sign_fixed_time(message, dkim_config, crate::time::now());
-    #[cfg(not(feature = "web"))]
-    dkim_sign_fixed_time(message, dkim_config, SystemTime::now());
+    dkim_sign_fixed_time(message, dkim_config, SystemTime::now())
 }

 fn dkim_sign_fixed_time(message: &mut Message, dkim_config: &DkimConfig, timestamp: SystemTime) {
@@ -380,7 +378,7 @@ 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(AsRef::as_ref),
+        dkim_config.headers.iter().map(|h| h.as_ref()),
        headers,
        dkim_config.canonicalization.header,
    );
@@ -490,14 +488,14 @@ 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 Visitor<'_> for ContentTypeVisitor {
+            impl<'de> Visitor<'de> 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(crate::time::now())
+        Self::new(SystemTime::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`] associated with sender.
+    This header contains [`Mailbox`][self::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`].
+    This header contains [`Mailboxes`][self::Mailboxes].

     */
    (From, "From")
@@ -135,7 +135,7 @@ mailboxes_header! {

    `Reply-To` header

-    This header contains [`Mailboxes`].
+    This header contains [`Mailboxes`][self::Mailboxes].

     */
    (ReplyTo, "Reply-To")
@@ -146,7 +146,7 @@ mailboxes_header! {

    `To` header

-    This header contains [`Mailboxes`].
+    This header contains [`Mailboxes`][self::Mailboxes].

     */
    (To, "To")
@@ -157,7 +157,7 @@ mailboxes_header! {

    `Cc` header

-    This header contains [`Mailboxes`].
+    This header contains [`Mailboxes`][self::Mailboxes].

     */
    (Cc, "Cc")
@@ -168,7 +168,7 @@ mailboxes_header! {

    `Bcc` header

-    This header contains [`Mailboxes`].
+    This header contains [`Mailboxes`][self::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("".to_owned()).is_err());
+        assert!(HeaderName::new_from_ascii(String::from("")).is_err());
    }

    #[test]
--- 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 Visitor<'_> for FieldVisitor {
+                impl<'de> Visitor<'de> 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("".to_owned()), "kayo@example.com".parse().unwrap())
+                Mailbox::new(Some("".into()), "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(crate::time::now())
+        self.date(SystemTime::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`])
+    /// Create message using mime body ([`MultiPart`][self::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`])
+    /// Create message using mime body ([`SinglePart`][self::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
    }
@@ -537,10 +537,7 @@ impl Message {
    /// Example:
    /// ```rust
    /// use lettre::{
-    ///     message::{
-    ///         dkim::{DkimConfig, DkimSigningAlgorithm, DkimSigningKey},
-    ///         header::ContentType,
-    ///     },
+    ///     message::dkim::{DkimConfig, DkimSigningAlgorithm, DkimSigningKey},
    ///     Message,
    /// };
    ///
@@ -549,7 +546,6 @@ 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-----
@@ -605,7 +601,7 @@ 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)
            }
        }
    }
@@ -769,7 +765,7 @@ mod test {
                continue;
            }

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

--- a/src/time.rs
+++ b/src/time.rs
@@ -1,18 +0,0 @@
-use std::time::SystemTime;
-
-#[cfg(feature = "web")]
-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
-    }
-
-    to_std_systemtime(web_time::SystemTime::now())
-}
-
-#[cfg(not(feature = "web"))]
-pub(crate) fn now() -> SystemTime {
-    SystemTime::now()
-}
--- a/src/transport/file/error.rs
+++ b/src/transport/file/error.rs
@@ -68,7 +68,7 @@ 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::{message::header::ContentType, FileTransport, Message, Transport};
+//! use lettre::{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!"))?;
 //!
-//! sender.send(&email)?;
+//! let result = sender.send(&email);
+//! assert!(result.is_ok());
 //! # Ok(())
 //! # }
 //!
@@ -44,7 +44,7 @@
 //! # fn main() -> Result<(), Box<dyn Error>> {
 //! use std::env::temp_dir;
 //!
-//! use lettre::{message::header::ContentType, FileTransport, Message, Transport};
+//! use lettre::{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!"))?;
 //!
-//! sender.send(&email)?;
+//! let result = sender.send(&email);
+//! assert!(result.is_ok());
 //! # Ok(())
 //! # }
 //!
@@ -73,9 +73,7 @@
 //! # async fn run() -> Result<(), Box<dyn Error>> {
 //! use std::env::temp_dir;
 //!
-//! use lettre::{
-//!     message::header::ContentType, AsyncFileTransport, AsyncTransport, Message, Tokio1Executor,
-//! };
+//! use lettre::{AsyncFileTransport, AsyncTransport, Message, Tokio1Executor};
 //!
 //! // Write to the local temp directory
 //! let sender = AsyncFileTransport::<Tokio1Executor>::new(temp_dir());
@@ -84,10 +82,10 @@
 //!     .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!"))?;
 //!
-//! sender.send(email).await?;
+//! let result = sender.send(email).await;
+//! assert!(result.is_ok());
 //! # Ok(())
 //! # }
 //! ```
@@ -101,10 +99,7 @@
 //! # async fn run() -> Result<(), Box<dyn Error>> {
 //! use std::env::temp_dir;
 //!
-//! use lettre::{
-//!     message::header::ContentType, AsyncFileTransport, AsyncStd1Executor, AsyncTransport,
-//!     Message,
-//! };
+//! use lettre::{AsyncFileTransport, AsyncStd1Executor, AsyncTransport, Message};
 //!
 //! // Write to the local temp directory
 //! let sender = AsyncFileTransport::<AsyncStd1Executor>::new(temp_dir());
@@ -113,10 +108,10 @@
 //!     .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!"))?;
 //!
-//! sender.send(email).await?;
+//! let result = sender.send(email).await;
+//! assert!(result.is_ok());
 //! # Ok(())
 //! # }
 //! ```
@@ -130,7 +125,6 @@
 //! 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!
--- a/src/transport/mod.rs
+++ b/src/transport/mod.rs
@@ -56,17 +56,13 @@
 //! #
 //! # #[cfg(all(feature = "builder", feature = "smtp-transport"))]
 //! # fn main() -> Result<(), Box<dyn Error>> {
-//! use lettre::{
-//!     message::header::ContentType, transport::smtp::authentication::Credentials, Message,
-//!     SmtpTransport, Transport,
-//! };
+//! use lettre::{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());
--- 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::header::ContentType, Message, SendmailTransport, Transport};
+//! use lettre::{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();
-//! sender.send(&email)?;
+//! let result = sender.send(&email);
+//! assert!(result.is_ok());
 //! # Ok(())
 //! # }
 //!
@@ -34,8 +34,7 @@
 //! # #[cfg(all(feature = "tokio1", feature = "sendmail-transport", feature = "builder"))]
 //! # async fn run() -> Result<(), Box<dyn Error>> {
 //! use lettre::{
-//!     message::header::ContentType, AsyncSendmailTransport, AsyncTransport, Message,
-//!     SendmailTransport, Tokio1Executor,
+//!     AsyncSendmailTransport, AsyncTransport, Message, SendmailTransport, Tokio1Executor,
 //! };
 //!
 //! let email = Message::builder()
@@ -43,11 +42,11 @@
 //!     .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();
-//! sender.send(email).await?;
+//! let result = sender.send(email).await;
+//! assert!(result.is_ok());
 //! # Ok(())
 //! # }
 //! ```
@@ -59,17 +58,18 @@
 //! #
 //! # #[cfg(all(feature = "async-std1", feature = "sendmail-transport", feature = "builder"))]
 //! # async fn run() -> Result<(), Box<dyn Error>> {
-//! use lettre::{Message, AsyncTransport, AsyncStd1Executor,message::header::ContentType, AsyncSendmailTransport};
+//! use lettre::{Message, AsyncTransport, AsyncStd1Executor, 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").header(ContentType::TEXT_PLAIN)
+//!     .subject("Happy new year")
 //!     .body(String::from("Be happy!"))?;
 //!
 //! let sender = AsyncSendmailTransport::<AsyncStd1Executor>::new();
-//! sender.send(email).await?;
+//! let result = sender.send(email).await;
+//! assert!(result.is_ok());
 //! # 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
@@ -12,12 +12,6 @@ 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-tls",
-    feature = "async-std1-rustls-tls"
-))]
-use super::Tls;
 use super::{
    client::AsyncSmtpConnection, ClientId, Credentials, Error, Mechanism, Response, SmtpInfo,
 };
@@ -30,30 +24,6 @@ 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")]
@@ -75,7 +45,7 @@ impl AsyncTransport for AsyncSmtpTransport<Tokio1Executor> {
        let result = conn.send(envelope, email).await?;

        #[cfg(not(feature = "pool"))]
-        conn.abort().await;
+        conn.quit().await?;

        Ok(result)
    }
@@ -191,72 +161,54 @@ where

    /// Creates a `AsyncSmtpTransportBuilder` from a connection URL
    ///
-    /// The protocol, credentials, host, port and EHLO name can be provided
-    /// in a single URL. This may be simpler than having to configure SMTP
-    /// through multiple configuration parameters and then having to pass
-    /// those options to lettre.
+    /// The 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 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
-    /// # let _ = 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:
+    /// <table>
+    ///   <thead>
+    ///     <tr>
+    ///       <th>scheme</th>
+    ///       <th>tls parameter</th>
+    ///       <th>example</th>
+    ///       <th>remarks</th>
+    ///     </tr>
+    ///   </thead>
+    ///   <tbody>
+    ///     <tr>
+    ///      <td>smtps</td>
+    ///      <td>-</td>
+    ///      <td>smtps://smtp.example.com</td>
+    ///      <td>SMTP over TLS, recommended method</td>
+    ///     </tr>
+    ///     <tr>
+    ///      <td>smtp</td>
+    ///      <td>required</td>
+    ///      <td>smtp://smtp.example.com?tls=required</td>
+    ///      <td>SMTP with STARTTLS required, when SMTP over TLS is not available</td>
+    ///     </tr>
+    ///     <tr>
+    ///      <td>smtp</td>
+    ///      <td>opportunistic</td>
+    ///      <td>smtp://smtp.example.com?tls=opportunistic</td>
+    ///      <td>
+    ///         SMTP with optionally STARTTLS when supported by the server.
+    ///         Caution: this method is vulnerable to a man-in-the-middle attack.
+    ///         Not recommended for production use.
+    ///       </td>
+    ///     </tr>
+    ///     <tr>
+    ///      <td>smtp</td>
+    ///      <td>-</td>
+    ///      <td>smtp://smtp.example.com</td>
+    ///      <td>Unencrypted SMTP, not recommended for production use.</td>
+    ///     </tr>
+    ///   </tbody>
+    /// </table>
    ///
    /// ```rust,no_run
    /// use lettre::{
@@ -280,11 +232,15 @@ where
    /// let mailer: AsyncSmtpTransport<Tokio1Executor> =
    ///     AsyncSmtpTransport::<Tokio1Executor>::from_url(
    ///         "smtps://username:password@smtp.example.com:465",
-    ///     )?
+    ///     )
+    ///     .unwrap()
    ///     .build();
    ///
    /// // Send the email
-    /// mailer.send(email).await?;
+    /// match mailer.send(email).await {
+    ///     Ok(_) => println!("Email sent successfully!"),
+    ///     Err(e) => panic!("Could not send email: {e:?}"),
+    /// }
    /// # Ok(())
    /// # }
    /// ```
@@ -367,7 +323,7 @@ impl AsyncSmtpTransportBuilder {
        self
    }

-    /// Set the authentication credentials to use
+    /// Set the authentication mechanism to use
    pub fn credentials(mut self, credentials: Credentials) -> Self {
        self.info.credentials = Some(credentials);
        self
@@ -380,17 +336,6 @@ 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
@@ -403,17 +348,6 @@ 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",
@@ -427,7 +361,7 @@ impl AsyncSmtpTransportBuilder {
            feature = "async-std1-rustls-tls"
        )))
    )]
-    pub fn tls(mut self, tls: Tls) -> Self {
+    pub fn tls(mut self, tls: super::Tls) -> Self {
        self.info.tls = tls;
        self
    }
--- a/src/transport/smtp/authentication.rs
+++ b/src/transport/smtp/authentication.rs
@@ -98,17 +98,13 @@ impl Mechanism {
                let decoded_challenge = challenge
                    .ok_or_else(|| error::client("This mechanism does expect a challenge"))?;

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

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

@@ -125,15 +121,6 @@ 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};
@@ -168,23 +155,6 @@ 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
@@ -10,34 +10,21 @@ use super::{AsyncNetworkStream, ClientCodec, TlsParameters};
 use crate::{
    transport::smtp::{
        authentication::{Credentials, Mechanism},
+        client::{ConnectionState, ConnectionWrapper},
        commands::{Auth, Data, Ehlo, Mail, Noop, Quit, Rcpt, Starttls},
-        error,
-        error::Error,
+        error::{self, Error},
        extension::{ClientId, Extension, MailBodyParameter, MailParameter, ServerInfo},
        response::{parse_response, Response},
    },
    Envelope,
 };

-macro_rules! try_smtp (
-    ($err: expr, $client: ident) => ({
-        match $err {
-            Ok(val) => val,
-            Err(err) => {
-                $client.abort().await;
-                return Err(From::from(err))
-            },
-        }
-    })
-);
-
 /// Structure that implements the SMTP client
 pub struct AsyncSmtpConnection {
    /// TCP stream between client and server
-    /// Value is None before connection
-    stream: BufReader<AsyncNetworkStream>,
-    /// Panic state
-    panic: bool,
+    stream: ConnectionWrapper<BufReader<AsyncNetworkStream>>,
+    /// Whether QUIT has been sent
+    sent_quit: bool,
    /// Information about the server
    server_info: ServerInfo,
 }
@@ -86,7 +73,8 @@ impl AsyncSmtpConnection {
    ///     Some(TlsParameters::new("example.com".to_owned())?),
    ///     None,
    /// )
-    /// .await?;
+    /// .await
+    /// .unwrap();
    /// # Ok(())
    /// # }
    /// ```
@@ -124,8 +112,8 @@ impl AsyncSmtpConnection {
    ) -> Result<AsyncSmtpConnection, Error> {
        let stream = BufReader::new(stream);
        let mut conn = AsyncSmtpConnection {
-            stream,
-            panic: false,
+            stream: ConnectionWrapper::new(stream),
+            sent_quit: false,
            server_info: ServerInfo::default(),
        };
        // TODO log
@@ -169,30 +157,28 @@ impl AsyncSmtpConnection {
            mail_options.push(MailParameter::Body(MailBodyParameter::EightBitMime));
        }

-        try_smtp!(
-            self.command(Mail::new(envelope.from().cloned(), mail_options))
-                .await,
-            self
-        );
+        self.command(Mail::new(envelope.from().cloned(), mail_options))
+            .await?;

        // Recipient
        for to_address in envelope.to() {
-            try_smtp!(
-                self.command(Rcpt::new(to_address.clone(), vec![])).await,
-                self
-            );
+            self.command(Rcpt::new(to_address.clone(), vec![])).await?;
        }

        // Data
-        try_smtp!(self.command(Data).await, self);
+        self.command(Data).await?;

        // Message content
-        let result = try_smtp!(self.message(email).await, self);
+        let result = self.message(email).await?;
        Ok(result)
    }

    pub fn has_broken(&self) -> bool {
-        self.panic
+        self.sent_quit
+            || matches!(
+                self.stream.state(),
+                ConnectionState::BrokenConnection | ConnectionState::BrokenResponse
+            )
    }

    pub fn can_starttls(&self) -> bool {
@@ -212,12 +198,14 @@ impl AsyncSmtpConnection {
        hello_name: &ClientId,
    ) -> Result<(), Error> {
        if self.server_info.supports_feature(Extension::StartTls) {
-            try_smtp!(self.command(Starttls).await, self);
-            self.stream.get_mut().upgrade_tls(tls_parameters).await?;
+            self.command(Starttls).await?;
+            self.stream
+                .async_op(|stream| stream.get_mut().upgrade_tls(tls_parameters))
+                .await?;
            #[cfg(feature = "tracing")]
            tracing::debug!("connection encrypted");
            // Send EHLO again
-            try_smtp!(self.ehlo(hello_name).await, self);
+            self.ehlo(hello_name).await?;
            Ok(())
        } else {
            Err(error::client("STARTTLS is not supported on this server"))
@@ -226,32 +214,39 @@ impl AsyncSmtpConnection {

    /// Send EHLO and update server info
    async fn ehlo(&mut self, hello_name: &ClientId) -> Result<(), Error> {
-        let ehlo_response = try_smtp!(self.command(Ehlo::new(hello_name.clone())).await, self);
-        self.server_info = try_smtp!(ServerInfo::from_response(&ehlo_response), self);
+        let ehlo_response = self.command(Ehlo::new(hello_name.clone())).await?;
+        self.server_info = ServerInfo::from_response(&ehlo_response)?;
        Ok(())
    }

    pub async fn quit(&mut self) -> Result<Response, Error> {
-        Ok(try_smtp!(self.command(Quit).await, self))
+        self.sent_quit = true;
+        self.command(Quit).await
    }

    pub async fn abort(&mut self) {
        // Only try to quit if we are not already broken
-        if !self.panic {
-            self.panic = true;
-            let _ = self.command(Quit).await;
+        // `write` already rejects writes if the connection state if bad
+        if !self.sent_quit {
+            let _ = self.quit().await;
+        }
+
+        if !matches!(self.stream.state(), ConnectionState::BrokenConnection) {
+            let _ = self
+                .stream
+                .async_op(|stream| async { stream.close().await.map_err(error::network) })
+                .await;
        }
-        let _ = self.stream.close().await;
    }

    /// Sets the underlying stream
    pub fn set_stream(&mut self, stream: AsyncNetworkStream) {
-        self.stream = BufReader::new(stream);
+        self.stream = ConnectionWrapper::new(BufReader::new(stream));
    }

    /// Tells if the underlying stream is currently encrypted
    pub fn is_encrypted(&self) -> bool {
-        self.stream.get_ref().is_encrypted()
+        self.stream.get_ref().get_ref().is_encrypted()
    }

    /// Checks if the server is connected using the NOOP SMTP command
@@ -278,15 +273,13 @@ impl AsyncSmtpConnection {

        while challenges > 0 && response.has_code(334) {
            challenges -= 1;
-            response = try_smtp!(
-                self.command(Auth::new_from_response(
+            response = self
+                .command(Auth::new_from_response(
                    mechanism,
                    credentials.clone(),
                    &response,
                )?)
-                .await,
-                self
-            );
+                .await?;
        }

        if challenges == 0 {
@@ -315,15 +308,17 @@ impl AsyncSmtpConnection {
    /// Writes a string to the server
    async fn write(&mut self, string: &[u8]) -> Result<(), Error> {
        self.stream
-            .get_mut()
-            .write_all(string)
-            .await
-            .map_err(error::network)?;
+            .async_op(|stream| async {
+                stream
+                    .get_mut()
+                    .write_all(string)
+                    .await
+                    .map_err(error::network)
+            })
+            .await?;
        self.stream
-            .get_mut()
-            .flush()
-            .await
-            .map_err(error::network)?;
+            .async_op(|stream| async { stream.get_mut().flush().await.map_err(error::network) })
+            .await?;

        #[cfg(feature = "tracing")]
        tracing::debug!("Wrote: {}", escape_crlf(&String::from_utf8_lossy(string)));
@@ -336,9 +331,10 @@ impl AsyncSmtpConnection {

        while self
            .stream
-            .read_line(&mut buffer)
-            .await
-            .map_err(error::network)?
+            .async_op(|stream| async {
+                stream.read_line(&mut buffer).await.map_err(error::network)
+            })
+            .await?
            > 0
        {
            #[cfg(feature = "tracing")]
@@ -355,10 +351,12 @@ impl AsyncSmtpConnection {
                    }
                }
                Err(nom::Err::Failure(e)) => {
+                    self.stream.set_state(ConnectionState::BrokenResponse);
                    return Err(error::response(e.to_string()));
                }
                Err(nom::Err::Incomplete(_)) => { /* read more */ }
                Err(nom::Err::Error(e)) => {
+                    self.stream.set_state(ConnectionState::BrokenResponse);
                    return Err(error::response(e.to_string()));
                }
            }
@@ -370,28 +368,12 @@ impl AsyncSmtpConnection {
    /// The X509 certificate of the server (DER encoded)
    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
    pub fn peer_certificate(&self) -> Result<Vec<u8>, Error> {
-        self.stream.get_ref().peer_certificate()
-    }
-
-    /// 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")]
-    pub fn tls_verify_result(&self) -> Result<(), Error> {
-        self.stream.get_ref().tls_verify_result()
+        self.stream.get_ref().get_ref().peer_certificate()
    }

    /// All the X509 certificates of the chain (DER encoded)
    #[cfg(any(feature = "rustls-tls", feature = "boring-tls"))]
    pub fn certificate_chain(&self) -> Result<Vec<Vec<u8>>, Error> {
-        self.stream.get_ref().certificate_chain()
+        self.stream.get_ref().get_ref().certificate_chain()
    }
 }
--- a/src/transport/smtp/client/async_net.rs
+++ b/src/transport/smtp/client/async_net.rs
@@ -170,7 +170,7 @@ impl AsyncNetworkStream {
                            last_err = Some(io::Error::new(
                                io::ErrorKind::TimedOut,
                                "connection timed out",
-                            ));
+                            ))
                        }
                    }
                } else {
@@ -222,7 +222,7 @@ impl AsyncNetworkStream {
                        last_err = Some(io::Error::new(
                            io::ErrorKind::TimedOut,
                            "connection timed out",
-                        ));
+                        ))
                    }
                }
            }
@@ -270,8 +270,9 @@ impl AsyncNetworkStream {
            InnerAsyncNetworkStream::Tokio1Tcp(_) => {
                // get owned TcpStream
                let tcp_stream = mem::replace(&mut self.inner, InnerAsyncNetworkStream::None);
-                let InnerAsyncNetworkStream::Tokio1Tcp(tcp_stream) = tcp_stream else {
-                    unreachable!()
+                let tcp_stream = match tcp_stream {
+                    InnerAsyncNetworkStream::Tokio1Tcp(tcp_stream) => tcp_stream,
+                    _ => unreachable!(),
                };

                self.inner = Self::upgrade_tokio1_tls(tcp_stream, tls_parameters)
@@ -289,8 +290,9 @@ impl AsyncNetworkStream {
            InnerAsyncNetworkStream::AsyncStd1Tcp(_) => {
                // get owned TcpStream
                let tcp_stream = mem::replace(&mut self.inner, InnerAsyncNetworkStream::None);
-                let InnerAsyncNetworkStream::AsyncStd1Tcp(tcp_stream) = tcp_stream else {
-                    unreachable!()
+                let tcp_stream = match tcp_stream {
+                    InnerAsyncNetworkStream::AsyncStd1Tcp(tcp_stream) => tcp_stream,
+                    _ => unreachable!(),
                };

                self.inner = Self::upgrade_asyncstd1_tls(tcp_stream, tls_parameters)
@@ -429,30 +431,6 @@ impl AsyncNetworkStream {
        }
    }

-    #[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-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(_) => 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-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(_) => 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")]
--- a/src/transport/smtp/client/connection.rs
+++ b/src/transport/smtp/client/connection.rs
@@ -7,38 +7,25 @@ use std::{

 #[cfg(feature = "tracing")]
 use super::escape_crlf;
-use super::{ClientCodec, NetworkStream, TlsParameters};
+use super::{ClientCodec, ConnectionWrapper, NetworkStream, TlsParameters};
 use crate::{
    address::Envelope,
    transport::smtp::{
        authentication::{Credentials, Mechanism},
+        client::ConnectionState,
        commands::{Auth, Data, Ehlo, Mail, Noop, Quit, Rcpt, Starttls},
-        error,
-        error::Error,
+        error::{self, Error},
        extension::{ClientId, Extension, MailBodyParameter, MailParameter, ServerInfo},
        response::{parse_response, Response},
    },
 };

-macro_rules! try_smtp (
-    ($err: expr, $client: ident) => ({
-        match $err {
-            Ok(val) => val,
-            Err(err) => {
-                $client.abort();
-                return Err(From::from(err))
-            },
-        }
-    })
-);
-
 /// Structure that implements the SMTP client
 pub struct SmtpConnection {
    /// TCP stream between client and server
-    /// Value is None before connection
-    stream: BufReader<NetworkStream>,
-    /// Panic state
-    panic: bool,
+    stream: ConnectionWrapper<BufReader<NetworkStream>>,
+    /// Whether QUIT has been sent
+    sent_quit: bool,
    /// Information about the server
    server_info: ServerInfo,
 }
@@ -64,8 +51,8 @@ impl SmtpConnection {
        let stream = NetworkStream::connect(server, timeout, tls_parameters, local_address)?;
        let stream = BufReader::new(stream);
        let mut conn = SmtpConnection {
-            stream,
-            panic: false,
+            stream: ConnectionWrapper::new(stream),
+            sent_quit: false,
            server_info: ServerInfo::default(),
        };
        conn.set_timeout(timeout).map_err(error::network)?;
@@ -110,26 +97,27 @@ impl SmtpConnection {
            mail_options.push(MailParameter::Body(MailBodyParameter::EightBitMime));
        }

-        try_smtp!(
-            self.command(Mail::new(envelope.from().cloned(), mail_options)),
-            self
-        );
+        self.command(Mail::new(envelope.from().cloned(), mail_options))?;

        // Recipient
        for to_address in envelope.to() {
-            try_smtp!(self.command(Rcpt::new(to_address.clone(), vec![])), self);
+            self.command(Rcpt::new(to_address.clone(), vec![]))?;
        }

        // Data
-        try_smtp!(self.command(Data), self);
+        self.command(Data)?;

        // Message content
-        let result = try_smtp!(self.message(email), self);
+        let result = self.message(email)?;
        Ok(result)
    }

    pub fn has_broken(&self) -> bool {
-        self.panic
+        self.sent_quit
+            || matches!(
+                self.stream.state(),
+                ConnectionState::BrokenConnection | ConnectionState::BrokenResponse
+            )
    }

    pub fn can_starttls(&self) -> bool {
@@ -145,12 +133,13 @@ impl SmtpConnection {
        if self.server_info.supports_feature(Extension::StartTls) {
            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
            {
-                try_smtp!(self.command(Starttls), self);
-                self.stream.get_mut().upgrade_tls(tls_parameters)?;
+                self.command(Starttls)?;
+                self.stream
+                    .sync_op(|stream| stream.get_mut().upgrade_tls(tls_parameters))?;
                #[cfg(feature = "tracing")]
                tracing::debug!("connection encrypted");
                // Send EHLO again
-                try_smtp!(self.ehlo(hello_name), self);
+                self.ehlo(hello_name)?;
                Ok(())
            }
            #[cfg(not(any(
@@ -168,38 +157,47 @@ impl SmtpConnection {

    /// Send EHLO and update server info
    fn ehlo(&mut self, hello_name: &ClientId) -> Result<(), Error> {
-        let ehlo_response = try_smtp!(self.command(Ehlo::new(hello_name.clone())), self);
-        self.server_info = try_smtp!(ServerInfo::from_response(&ehlo_response), self);
+        let ehlo_response = self.command(Ehlo::new(hello_name.clone()))?;
+        self.server_info = ServerInfo::from_response(&ehlo_response)?;
        Ok(())
    }

    pub fn quit(&mut self) -> Result<Response, Error> {
-        Ok(try_smtp!(self.command(Quit), self))
+        self.sent_quit = true;
+        self.command(Quit)
    }

    pub fn abort(&mut self) {
        // Only try to quit if we are not already broken
-        if !self.panic {
-            self.panic = true;
-            let _ = self.command(Quit);
+        // `write` already rejects writes if the connection state if bad
+        if !self.sent_quit {
+            let _ = self.quit();
+        }
+
+        if !matches!(self.stream.state(), ConnectionState::BrokenConnection) {
+            let _ = self.stream.sync_op(|stream| {
+                stream
+                    .get_mut()
+                    .shutdown(std::net::Shutdown::Both)
+                    .map_err(error::network)
+            });
        }
-        let _ = self.stream.get_mut().shutdown(std::net::Shutdown::Both);
    }

    /// Sets the underlying stream
    pub fn set_stream(&mut self, stream: NetworkStream) {
-        self.stream = BufReader::new(stream);
+        self.stream = ConnectionWrapper::new(BufReader::new(stream));
    }

    /// Tells if the underlying stream is currently encrypted
    pub fn is_encrypted(&self) -> bool {
-        self.stream.get_ref().is_encrypted()
+        self.stream.get_ref().get_ref().is_encrypted()
    }

    /// Set timeout
    pub fn set_timeout(&mut self, duration: Option<Duration>) -> io::Result<()> {
-        self.stream.get_mut().set_read_timeout(duration)?;
-        self.stream.get_mut().set_write_timeout(duration)
+        self.stream.get_mut().get_mut().set_read_timeout(duration)?;
+        self.stream.get_mut().get_mut().set_write_timeout(duration)
    }

    /// Checks if the server is connected using the NOOP SMTP command
@@ -224,14 +222,11 @@ impl SmtpConnection {

        while challenges > 0 && response.has_code(334) {
            challenges -= 1;
-            response = try_smtp!(
-                self.command(Auth::new_from_response(
-                    mechanism,
-                    credentials.clone(),
-                    &response,
-                )?),
-                self
-            );
+            response = self.command(Auth::new_from_response(
+                mechanism,
+                credentials.clone(),
+                &response,
+            )?)?;
        }

        if challenges == 0 {
@@ -261,10 +256,9 @@ impl SmtpConnection {
    /// Writes a string to the server
    fn write(&mut self, string: &[u8]) -> Result<(), Error> {
        self.stream
-            .get_mut()
-            .write_all(string)
-            .map_err(error::network)?;
-        self.stream.get_mut().flush().map_err(error::network)?;
+            .sync_op(|stream| stream.get_mut().write_all(string).map_err(error::network))?;
+        self.stream
+            .sync_op(|stream| stream.get_mut().flush().map_err(error::network))?;

        #[cfg(feature = "tracing")]
        tracing::debug!("Wrote: {}", escape_crlf(&String::from_utf8_lossy(string)));
@@ -275,7 +269,11 @@ impl SmtpConnection {
    pub fn read_response(&mut self) -> Result<Response, Error> {
        let mut buffer = String::with_capacity(100);

-        while self.stream.read_line(&mut buffer).map_err(error::network)? > 0 {
+        while self
+            .stream
+            .sync_op(|stream| stream.read_line(&mut buffer).map_err(error::network))?
+            > 0
+        {
            #[cfg(feature = "tracing")]
            tracing::debug!("<< {}", escape_crlf(&buffer));
            match parse_response(&buffer) {
@@ -290,10 +288,12 @@ impl SmtpConnection {
                    };
                }
                Err(nom::Err::Failure(e)) => {
+                    self.stream.set_state(ConnectionState::BrokenResponse);
                    return Err(error::response(e.to_string()));
                }
                Err(nom::Err::Incomplete(_)) => { /* read more */ }
                Err(nom::Err::Error(e)) => {
+                    self.stream.set_state(ConnectionState::BrokenResponse);
                    return Err(error::response(e.to_string()));
                }
            }
@@ -305,28 +305,12 @@ impl SmtpConnection {
    /// The X509 certificate of the server (DER encoded)
    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
    pub fn peer_certificate(&self) -> Result<Vec<u8>, Error> {
-        self.stream.get_ref().peer_certificate()
-    }
-
-    /// 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")]
-    pub fn tls_verify_result(&self) -> Result<(), Error> {
-        self.stream.get_ref().tls_verify_result()
+        self.stream.get_ref().get_ref().peer_certificate()
    }

    /// All the X509 certificates of the chain (DER encoded)
    #[cfg(any(feature = "rustls-tls", feature = "boring-tls"))]
    pub fn certificate_chain(&self) -> Result<Vec<Vec<u8>>, Error> {
-        self.stream.get_ref().certificate_chain()
+        self.stream.get_ref().get_ref().certificate_chain()
    }
 }
--- a/src/transport/smtp/client/mod.rs
+++ b/src/transport/smtp/client/mod.rs
@@ -24,6 +24,8 @@

 #[cfg(feature = "serde")]
 use std::fmt::Debug;
+#[cfg(any(feature = "tokio1", feature = "async-std1"))]
+use std::future::Future;

 #[cfg(any(feature = "tokio1", feature = "async-std1"))]
 pub use self::async_connection::AsyncSmtpConnection;
@@ -40,6 +42,7 @@ pub use self::{
    connection::SmtpConnection,
    tls::{Certificate, CertificateStore, Identity, Tls, TlsParameters, TlsParametersBuilder},
 };
+use super::{error, Error};

 #[cfg(any(feature = "tokio1", feature = "async-std1"))]
 mod async_connection;
@@ -49,6 +52,99 @@ mod connection;
 mod net;
 mod tls;

+#[derive(Debug)]
+pub(super) struct ConnectionWrapper<C> {
+    conn: C,
+    state: ConnectionState,
+}
+
+impl<C> ConnectionWrapper<C> {
+    pub(super) fn new(conn: C) -> Self {
+        Self {
+            conn,
+            state: ConnectionState::ProbablyConnected,
+        }
+    }
+
+    pub(super) fn get_ref(&self) -> &C {
+        &self.conn
+    }
+
+    pub(super) fn get_mut(&mut self) -> &mut C {
+        &mut self.conn
+    }
+
+    pub(super) fn state(&self) -> ConnectionState {
+        self.state
+    }
+
+    pub(super) fn set_state(&mut self, state: ConnectionState) {
+        self.state = state;
+    }
+
+    pub(super) fn sync_op<F, T>(&mut self, f: F) -> Result<T, Error>
+    where
+        F: FnOnce(&mut C) -> Result<T, Error>,
+    {
+        if !matches!(
+            self.state,
+            ConnectionState::ProbablyConnected | ConnectionState::BrokenResponse
+        ) {
+            return Err(error::client(
+                "attempted to send operation to broken connection",
+            ));
+        }
+
+        self.state = ConnectionState::Writing;
+        match f(&mut self.conn) {
+            Ok(t) => {
+                self.state = ConnectionState::ProbablyConnected;
+                Ok(t)
+            }
+            Err(err) => {
+                self.state = ConnectionState::BrokenConnection;
+                Err(err)
+            }
+        }
+    }
+
+    #[cfg(any(feature = "tokio1", feature = "async-std1"))]
+    pub(super) async fn async_op<'a, F, Fut, T>(&'a mut self, f: F) -> Result<T, Error>
+    where
+        F: FnOnce(&'a mut C) -> Fut,
+        Fut: Future<Output = Result<T, Error>>,
+    {
+        if !matches!(
+            self.state,
+            ConnectionState::ProbablyConnected | ConnectionState::BrokenResponse
+        ) {
+            return Err(error::client(
+                "attempted to send operation to broken connection",
+            ));
+        }
+
+        self.state = ConnectionState::Writing;
+        match f(&mut self.conn).await {
+            Ok(t) => {
+                self.state = ConnectionState::ProbablyConnected;
+                Ok(t)
+            }
+            Err(err) => {
+                self.state = ConnectionState::BrokenConnection;
+                Err(err)
+            }
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+pub(super) enum ConnectionState {
+    ProbablyConnected,
+    Writing,
+    BrokenResponse,
+    BrokenConnection,
+}
+
 /// The codec used for transparency
 #[derive(Debug)]
 struct ClientCodec {
--- a/src/transport/smtp/client/net.rs
+++ b/src/transport/smtp/client/net.rs
@@ -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),
                    }
                }
@@ -160,8 +160,9 @@ impl NetworkStream {
            InnerNetworkStream::Tcp(_) => {
                // get owned TcpStream
                let tcp_stream = mem::replace(&mut self.inner, InnerNetworkStream::None);
-                let InnerNetworkStream::Tcp(tcp_stream) = tcp_stream else {
-                    unreachable!()
+                let tcp_stream = match tcp_stream {
+                    InnerNetworkStream::Tcp(tcp_stream) => tcp_stream,
+                    _ => unreachable!(),
                };

                self.inner = Self::upgrade_tls_impl(tcp_stream, tls_parameters)?;
@@ -222,22 +223,6 @@ impl NetworkStream {
        }
    }

-    #[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-tls")]
-            InnerNetworkStream::RustlsTls(_) => 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-tls", feature = "boring-tls"))]
    pub fn certificate_chain(&self) -> Result<Vec<Vec<u8>>, Error> {
        match &self.inner {
@@ -384,7 +369,7 @@ 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
@@ -59,61 +59,27 @@ pub enum TlsVersion {
    Tlsv13,
 }

-/// 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.
+/// How to apply TLS to a client connection
 #[derive(Clone)]
 #[allow(missing_copy_implementations)]
 pub enum Tls {
-    /// 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.
+    /// Insecure connection only (for testing purposes)
    None,
-    /// 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.
+    /// Start with insecure connection and use `STARTTLS` when available
    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
    #[cfg_attr(
        docsrs,
        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
    )]
    Opportunistic(TlsParameters),
-    /// 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.
+    /// Start with insecure connection and require `STARTTLS`
    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
    #[cfg_attr(
        docsrs,
        doc(cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls")))
    )]
    Required(TlsParameters),
-    /// 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.
+    /// Use TLS wrapped connection
    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
    #[cfg_attr(
        docsrs,
@@ -423,7 +389,7 @@ impl TlsParametersBuilder {
        let mut root_cert_store = RootCertStore::empty();

        #[cfg(feature = "rustls-native-certs")]
-        fn load_native_roots(store: &mut RootCertStore) {
+        fn load_native_roots(store: &mut RootCertStore) -> Result<(), Error> {
            let rustls_native_certs::CertificateResult { certs, errors, .. } =
                rustls_native_certs::load_native_certs();
            let errors_len = errors.len();
@@ -433,6 +399,7 @@ impl TlsParametersBuilder {
            tracing::debug!(
                "loaded platform certs with {errors_len} failing to load, {added} valid and {ignored} ignored (invalid) certs"
            );
+            Ok(())
        }

        #[cfg(feature = "rustls-tls")]
@@ -443,7 +410,7 @@ impl TlsParametersBuilder {
        match self.cert_store {
            CertificateStore::Default => {
                #[cfg(feature = "rustls-native-certs")]
-                load_native_roots(&mut root_cert_store);
+                load_native_roots(&mut root_cert_store)?;
                #[cfg(not(feature = "rustls-native-certs"))]
                load_webpki_roots(&mut root_cert_store);
            }
@@ -661,11 +628,10 @@ impl Identity {
    #[cfg(feature = "rustls-tls")]
    fn from_pem_rustls_tls(
        pem: &[u8],
-        mut key: &[u8],
+        key: &[u8],
    ) -> Result<(Vec<CertificateDer<'static>>, PrivateKeyDer<'static>), Error> {
-        let key = rustls_pemfile::private_key(&mut key)
-            .map_err(error::tls)?
-            .ok_or_else(|| error::tls("no private key found"))?;
+        let mut key = key;
+        let key = rustls_pemfile::private_key(&mut key).unwrap().unwrap();
        Ok((vec![pem.to_owned().into()], key))
    }

--- a/src/transport/smtp/connection_url.rs
+++ b/src/transport/smtp/connection_url.rs
@@ -1,5 +1,3 @@
-use std::borrow::Cow;
-
 use url::Url;

 #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
@@ -64,7 +62,7 @@ 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
@@ -86,26 +84,26 @@ pub(crate) fn from_connection_url<B: TransportBuilder>(connection_url: &str) ->
        ("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"))]
        ("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"))]
        ("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 {
@@ -117,7 +115,7 @@ 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::into_owned)
+                .map(|cow| cow.into_owned())
                .map_err(error::connection)
        };
        let credentials = Credentials::new(
--- a/src/transport/smtp/error.rs
+++ b/src/transport/smtp/error.rs
@@ -142,7 +142,7 @@ impl fmt::Display for Error {
            Kind::Permanent(code) => {
                write!(f, "permanent error ({code})")?;
            }
-        }
+        };

        if let Some(e) = &self.inner.source {
            write!(f, ": {e}")?;
--- a/src/transport/smtp/extension.rs
+++ b/src/transport/smtp/extension.rs
@@ -129,8 +129,9 @@ impl Display for ServerInfo {
 impl ServerInfo {
    /// Parses a EHLO response to create a `ServerInfo`
    pub fn from_response(response: &Response) -> Result<ServerInfo, Error> {
-        let Some(name) = response.first_word() else {
-            return Err(error::response("Could not read server name"));
+        let name = match response.first_word() {
+            Some(name) => name,
+            None => return Err(error::response("Could not read server name")),
        };

        let mut features: HashSet<Extension> = HashSet::new();
@@ -168,7 +169,7 @@ impl ServerInfo {
                    }
                }
                _ => (),
-            }
+            };
        }

        Ok(ServerInfo {
--- a/src/transport/smtp/mod.rs
+++ b/src/transport/smtp/mod.rs
@@ -26,17 +26,43 @@
 //!
 //! The relay server can be the local email server, a specific host or a third-party service.
 //!
-//! #### Simple example with authentication
+//! #### Simple example
 //!
-//! A good starting point for sending emails via SMTP relay is to
-//! do the following:
+//! This is the most basic example of usage:
+//!
+//! ```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")))]
 //! # fn test() -> Result<(), Box<dyn std::error::Error>> {
 //! use lettre::{
-//!     message::header::ContentType,
-//!     transport::smtp::authentication::{Credentials, Mechanism},
+//!     transport::smtp::{
+//!         authentication::{Credentials, Mechanism},
+//!         PoolConfig,
+//!     },
 //!     Message, SmtpTransport, Transport,
 //! };
 //!
@@ -45,39 +71,35 @@
 //!     .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 the SMTPS transport
-//! let sender = SmtpTransport::relay("smtp.example.com")?
+//! // Create TLS transport on port 587 with STARTTLS
+//! let sender = SmtpTransport::starttls_relay("smtp.example.com")?
 //!     // Add credentials for authentication
 //!     .credentials(Credentials::new(
 //!         "username".to_owned(),
 //!         "password".to_owned(),
 //!     ))
-//!     // Optionally configure expected authentication mechanism
+//!     // 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
-//! sender.send(&email)?;
+//! let result = sender.send(&email);
+//! assert!(result.is_ok());
 //! # Ok(())
 //! # }
 //! ```
 //!
-//! #### 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`].
+//! You can specify custom TLS settings:
 //!
 //! ```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::header::ContentType,
-//!     transport::smtp::authentication::{Credentials, Mechanism},
+//!     transport::smtp::client::{Tls, TlsParameters},
 //!     Message, SmtpTransport, Transport,
 //! };
 //!
@@ -86,106 +108,25 @@
 //!     .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 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-tls")))]
-//! # 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)
+//! // Custom TLS configuration
+//! let tls = TlsParameters::builder("smtp.example.com".to_owned())
+//!     .dangerous_accept_invalid_certs(true)
 //!     .build()?;
 //!
-//! // Create the SMTPS transport
+//! // Create TLS transport on port 465
 //! let sender = SmtpTransport::relay("smtp.example.com")?
-//!     .tls(Tls::Wrapper(tls))
+//!     // Custom TLS configuration
+//!     .tls(Tls::Required(tls))
 //!     .build();
 //!
 //! // Send the email via remote relay
-//! sender.send(&email)?;
+//! let result = sender.send(&email);
+//! assert!(result.is_ok());
 //! # 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-tls")))]
-//! # 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;

--- a/src/transport/smtp/pool/async_impl.rs
+++ b/src/transport/smtp/pool/async_impl.rs
@@ -78,7 +78,7 @@ 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) => {
@@ -109,7 +109,7 @@ impl<E: Executor> Pool<E> {
                                #[cfg(feature = "tracing")]
                                tracing::debug!("dropped {} idle connections", dropped.len());

-                                abort_concurrent(dropped.into_iter().map(ParkedConnection::unpark))
+                                abort_concurrent(dropped.into_iter().map(|conn| conn.unpark()))
                                    .await;
                            }
                        }
@@ -229,7 +229,7 @@ impl<E: Executor> Drop for Pool<E> {
                handle.shutdown().await;
            }

-            abort_concurrent(connections.into_iter().map(ParkedConnection::unpark)).await;
+            abort_concurrent(connections.into_iter().map(|conn| conn.unpark())).await;
        });
    }
 }
--- a/src/transport/smtp/pool/sync_impl.rs
+++ b/src/transport/smtp/pool/sync_impl.rs
@@ -72,7 +72,7 @@ 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) => {
@@ -109,7 +109,6 @@ impl Pool {
                            }
                        }

-                        drop(pool);
                        thread::sleep(idle_timeout);
                    }
                })
--- a/src/transport/smtp/transport.rs
+++ b/src/transport/smtp/transport.rs
@@ -11,31 +11,7 @@ use super::{ClientId, Credentials, Error, Mechanism, Response, SmtpConnection, S
 use super::{Tls, TlsParameters, SUBMISSIONS_PORT, SUBMISSION_PORT};
 use crate::{address::Envelope, Transport};

-/// 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`].
+/// Sends emails using the SMTP protocol
 #[cfg_attr(docsrs, doc(cfg(feature = "smtp-transport")))]
 #[derive(Clone)]
 pub struct SmtpTransport {
@@ -56,7 +32,7 @@ impl Transport for SmtpTransport {
        let result = conn.send(envelope, email)?;

        #[cfg(not(feature = "pool"))]
-        conn.abort();
+        conn.quit()?;

        Ok(result)
    }
@@ -139,72 +115,54 @@ impl SmtpTransport {

    /// Creates a `SmtpTransportBuilder` from a connection URL
    ///
-    /// The protocol, credentials, host, port and EHLO name can be provided
-    /// in a single URL. This may be simpler than having to configure SMTP
-    /// through multiple configuration parameters and then having to pass
-    /// those options to lettre.
+    /// The 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 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
-    /// # let _ = 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:
+    /// <table>
+    ///   <thead>
+    ///     <tr>
+    ///       <th>scheme</th>
+    ///       <th>tls parameter</th>
+    ///       <th>example</th>
+    ///       <th>remarks</th>
+    ///     </tr>
+    ///   </thead>
+    ///   <tbody>
+    ///     <tr>
+    ///      <td>smtps</td>
+    ///      <td>-</td>
+    ///      <td>smtps://smtp.example.com</td>
+    ///      <td>SMTP over TLS, recommended method</td>
+    ///     </tr>
+    ///     <tr>
+    ///      <td>smtp</td>
+    ///      <td>required</td>
+    ///      <td>smtp://smtp.example.com?tls=required</td>
+    ///      <td>SMTP with STARTTLS required, when SMTP over TLS is not available</td>
+    ///     </tr>
+    ///     <tr>
+    ///      <td>smtp</td>
+    ///      <td>opportunistic</td>
+    ///      <td>smtp://smtp.example.com?tls=opportunistic</td>
+    ///      <td>
+    ///         SMTP with optionally STARTTLS when supported by the server.
+    ///         Caution: this method is vulnerable to a man-in-the-middle attack.
+    ///         Not recommended for production use.
+    ///       </td>
+    ///     </tr>
+    ///     <tr>
+    ///      <td>smtp</td>
+    ///      <td>-</td>
+    ///      <td>smtp://smtp.example.com</td>
+    ///      <td>Unencrypted SMTP, not recommended for production use.</td>
+    ///     </tr>
+    ///   </tbody>
+    /// </table>
    ///
    /// ```rust,no_run
    /// use lettre::{
@@ -212,7 +170,6 @@ 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())
@@ -223,12 +180,15 @@ impl SmtpTransport {
    ///     .unwrap();
    ///
    /// // Open a remote connection to example
-    /// let mailer = SmtpTransport::from_url("smtps://username:password@smtp.example.com")?.build();
+    /// let mailer = SmtpTransport::from_url("smtps://username:password@smtp.example.com:465")
+    ///     .unwrap()
+    ///     .build();
    ///
    /// // Send the email
-    /// mailer.send(&email)?;
-    /// # Ok(())
-    /// # }
+    /// match mailer.send(&email) {
+    ///     Ok(_) => println!("Email sent successfully!"),
+    ///     Err(e) => panic!("Could not send email: {e:?}"),
+    /// }
    /// ```
    #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
    #[cfg_attr(
@@ -286,7 +246,7 @@ impl SmtpTransportBuilder {
        self
    }

-    /// Set the authentication credentials to use
+    /// Set the authentication mechanism to use
    pub fn credentials(mut self, credentials: Credentials) -> Self {
        self.info.credentials = Some(credentials);
        self
@@ -305,34 +265,12 @@ 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
-    ///
-    /// # ⚠️⚠️⚠️ 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-tls", feature = "boring-tls"))]
    #[cfg_attr(
        docsrs,
--- a/src/transport/smtp/util.rs
+++ b/src/transport/smtp/util.rs
@@ -6,7 +6,7 @@ use std::fmt::{Display, Formatter, Result as FmtResult};
 #[derive(Debug)]
 pub struct XText<'a>(pub &'a str);

-impl Display for XText<'_> {
+impl<'a> Display for XText<'a> {
    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
        let mut rest = self.0;
        while let Some(idx) = rest.find(|c| c < '!' || c == '+' || c == '=') {
@@ -38,7 +38,9 @@ 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
@@ -11,9 +11,7 @@
 //! ```rust
 //! # #[cfg(feature = "builder")]
 //! # {
-//! use lettre::{
-//!     message::header::ContentType, transport::stub::StubTransport, Message, Transport,
-//! };
+//! use lettre::{transport::stub::StubTransport, Message, Transport};
 //!
 //! # use std::error::Error;
 //! # fn try_main() -> Result<(), Box<dyn Error>> {
@@ -22,11 +20,11 @@
 //!     .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();
-//! sender.send(&email)?;
+//! let result = sender.send(&email);
+//! assert!(result.is_ok());
 //! assert_eq!(
 //!     sender.messages(),
 //!     vec![(