Prepare 0.11.7 (#961)

Bumps [rustls](https://github.com/rustls/rustls) from 0.23.3 to 0.23.5.
- [Release notes](https://github.com/rustls/rustls/releases)
- [Changelog](https://github.com/rustls/rustls/blob/main/CHANGELOG.md)
- [Commits](https://github.com/rustls/rustls/compare/v/0.23.3...v/0.23.5)

---
updated-dependencies:
- dependency-name: rustls
  dependency-type: direct:production
...

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

.gitignore

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

CHANGELOG.md

@@ -1,3 +1,55 @@
+<a name="v0.11.7"></a>
+### v0.11.7 (2024-04-23)
+
+#### Misc
+
+* Bump `hostname` to v0.4 ([#956])
+* Fix `tracing` message consistency ([#960])
+* Bump minimum required `rustls` to v0.23.5 ([#958])
+* Dropped use of `ref` syntax in the entire project ([#959])
+
+[#956]: https://github.com/lettre/lettre/pull/956
+[#958]: https://github.com/lettre/lettre/pull/958
+[#959]: https://github.com/lettre/lettre/pull/959
+[#960]: https://github.com/lettre/lettre/pull/960
+
+<a name="v0.11.6"></a>
+### v0.11.6 (2024-03-28)
+
+#### Bug fixes
+
+* Upgraded `email-encoding` to v0.3 - fixing multiple encoding bugs in the process ([#952])
+
+#### Misc
+
+* Updated copyright year in license ([#954])
+
+[#952]: https://github.com/lettre/lettre/pull/952
+[#954]: https://github.com/lettre/lettre/pull/954
+
+<a name="v0.11.5"></a>
+### v0.11.5 (2024-03-25)
+
+#### Features
+
+* Support SMTP SASL draft login challenge ([#911])
+* Add conversion from SMTP response code to integer ([#941])
+
+#### Misc
+
+* Upgrade `rustls` to v0.23 ([#950])
+* Bump `base64` to v0.22 ([#945])
+* Fix typos in documentation ([#943], [#944])
+* Add `Cargo.lock` ([#942])
+
+[#911]: https://github.com/lettre/lettre/pull/911
+[#941]: https://github.com/lettre/lettre/pull/941
+[#942]: https://github.com/lettre/lettre/pull/942
+[#943]: https://github.com/lettre/lettre/pull/943
+[#944]: https://github.com/lettre/lettre/pull/944
+[#945]: https://github.com/lettre/lettre/pull/945
+[#950]: https://github.com/lettre/lettre/pull/950
+
 <a name="v0.11.4"></a>
 ### v0.11.4 (2024-01-28)
 
@@ -244,7 +296,7 @@ Several breaking changes were made between 0.9 and 0.10, but changes should be s
 * Update `hostname` to 0.3
 * Update to `nom` 6
 * Replace `log` with `tracing`
-* Move CI to Github Actions
+* Move CI to GitHub Actions
 * Use criterion for benchmarks
 
 <a name="v0.9.2"></a>

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 = "0.11.4"
+version = "0.11.7"
 description = "Email client"
 readme = "README.md"
 homepage = "https://lettre.rs"
@@ -28,8 +28,8 @@ httpdate = { version = "1", optional = true }
 mime = { version = "0.3.4", optional = true }
 fastrand = { version = "2.0", optional = true }
 quoted_printable = { version = "0.5", optional = true }
-base64 = { version = "0.21", optional = true }
-email-encoding = { version = "0.2", optional = true }
+base64 = { version = "0.22", optional = true }
+email-encoding = { version = "0.3", optional = true }
 
 # file transport
 uuid = { version = "1", features = ["v4"], optional = true }
@@ -38,14 +38,14 @@ serde_json = { version = "1", optional = true }
 
 # smtp-transport
 nom = { version = "7", optional = true }
-hostname = { version = "0.3", optional = true } # feature
+hostname = { version = "0.4", optional = true } # feature
 socket2 = { version = "0.5.1", optional = true }
 url = { version = "2.4", optional = true }
 percent-encoding = { version = "2.3", optional = true }
 
 ## tls
 native-tls = { version = "0.2.5", optional = true } # feature
-rustls = { version = "0.22.1", optional = true }
+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 = "0.7", optional = true }
 webpki-roots = { version = "0.26", optional = true }
@@ -59,12 +59,12 @@ async-trait = { version = "0.1", optional = true }
 ## async-std
 async-std = { version = "1.8", optional = true }
 #async-native-tls = { version = "0.3.3", optional = true }
-futures-rustls = { version = "0.25", optional = true }
+futures-rustls = { version = "0.26", default-features = false, features = ["logging", "tls12", "ring"], optional = true }
 
 ## tokio
 tokio1_crate = { package = "tokio", version = "1", optional = true }
 tokio1_native_tls_crate = { package = "tokio-native-tls", version = "0.3", optional = true }
-tokio1_rustls = { package = "tokio-rustls", version = "0.25", optional = true }
+tokio1_rustls = { package = "tokio-rustls", version = "0.26", default-features = false, features = ["logging", "tls12", "ring"], optional = true }
 tokio1_boring = { package = "tokio-boring", version = "4", optional = true }
 
 ## dkim

LICENSE

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

README.md

@@ -28,8 +28,8 @@
 </div>
 
 <div align="center">
-  <a href="https://deps.rs/crate/lettre/0.11.4">
-    <img src="https://deps.rs/crate/lettre/0.11.4/status.svg"
+  <a href="https://deps.rs/crate/lettre/0.11.7">
+    <img src="https://deps.rs/crate/lettre/0.11.7/status.svg"
       alt="dependency status" />
   </a>
 </div>

examples/autoconfigure.rs

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

src/executor.rs

@@ -134,7 +134,7 @@ impl Executor for Tokio1Executor {
         #[allow(clippy::match_single_binding)]
         let tls_parameters = match tls {
             #[cfg(any(feature = "tokio1-native-tls", feature = "tokio1-rustls-tls"))]
-            Tls::Wrapper(ref tls_parameters) => Some(tls_parameters.clone()),
+            Tls::Wrapper(tls_parameters) => Some(tls_parameters.clone()),
             _ => None,
         };
         #[allow(unused_mut)]
@@ -149,12 +149,12 @@ impl Executor for Tokio1Executor {
 
         #[cfg(any(feature = "tokio1-native-tls", feature = "tokio1-rustls-tls"))]
         match tls {
-            Tls::Opportunistic(ref tls_parameters) => {
+            Tls::Opportunistic(tls_parameters) => {
                 if conn.can_starttls() {
                     conn.starttls(tls_parameters.clone(), hello_name).await?;
                 }
             }
-            Tls::Required(ref tls_parameters) => {
+            Tls::Required(tls_parameters) => {
                 conn.starttls(tls_parameters.clone(), hello_name).await?;
             }
             _ => (),
@@ -231,7 +231,7 @@ impl Executor for AsyncStd1Executor {
         #[allow(clippy::match_single_binding)]
         let tls_parameters = match tls {
             #[cfg(any(feature = "async-std1-native-tls", feature = "async-std1-rustls-tls"))]
-            Tls::Wrapper(ref tls_parameters) => Some(tls_parameters.clone()),
+            Tls::Wrapper(tls_parameters) => Some(tls_parameters.clone()),
             _ => None,
         };
         #[allow(unused_mut)]
@@ -245,12 +245,12 @@ impl Executor for AsyncStd1Executor {
 
         #[cfg(any(feature = "async-std1-native-tls", feature = "async-std1-rustls-tls"))]
         match tls {
-            Tls::Opportunistic(ref tls_parameters) => {
+            Tls::Opportunistic(tls_parameters) => {
                 if conn.can_starttls() {
                     conn.starttls(tls_parameters.clone(), hello_name).await?;
                 }
             }
-            Tls::Required(ref tls_parameters) => {
+            Tls::Required(tls_parameters) => {
                 conn.starttls(tls_parameters.clone(), hello_name).await?;
             }
             _ => (),

src/lib.rs

@@ -109,7 +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/0.11.4")]
+#![doc(html_root_url = "https://docs.rs/crate/lettre/0.11.7")]
 #![doc(html_favicon_url = "https://lettre.rs/favicon.ico")]
 #![doc(html_logo_url = "https://avatars0.githubusercontent.com/u/15113230?v=4")]
 #![forbid(unsafe_code)]

src/message/dkim.rs

@@ -2,7 +2,6 @@ use std::{
     borrow::Cow,
     error::Error as StdError,
     fmt::{self, Display},
-    iter::IntoIterator,
     time::SystemTime,
 };
 

src/message/header/content_disposition.rs

@@ -1,6 +1,6 @@
 use std::fmt::Write;
 
-use email_encoding::headers::EmailWriter;
+use email_encoding::headers::writer::EmailWriter;
 
 use super::{Header, HeaderName, HeaderValue};
 use crate::BoxError;
@@ -38,10 +38,10 @@ impl ContentDisposition {
         let mut encoded_value = String::new();
         let line_len = "Content-Disposition: ".len();
         {
-            let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false, false);
+            let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false);
             w.write_str(kind).expect("writing `kind` returned an error");
             w.write_char(';').expect("writing `;` returned an error");
-            w.optional_breakpoint();
+            w.space();
 
             email_encoding::headers::rfc2231::encode("filename", file_name, &mut w)
                 .expect("some Write implementation returned an error");

src/message/header/mailbox.rs

@@ -1,4 +1,4 @@
-use email_encoding::headers::EmailWriter;
+use email_encoding::headers::writer::EmailWriter;
 
 use super::{Header, HeaderName, HeaderValue};
 use crate::{
@@ -31,7 +31,7 @@ macro_rules! mailbox_header {
                 let mut encoded_value = String::new();
                 let line_len = $header_name.len() + ": ".len();
                 {
-                    let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false, false);
+                    let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false);
                     self.0.encode(&mut w).expect("writing `Mailbox` returned an error");
                 }
 
@@ -81,7 +81,7 @@ macro_rules! mailboxes_header {
                 let mut encoded_value = String::new();
                 let line_len = $header_name.len() + ": ".len();
                 {
-                    let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false, false);
+                    let mut w = EmailWriter::new(&mut encoded_value, line_len, 0, false);
                     self.0.encode(&mut w).expect("writing `Mailboxes` returned an error");
                 }
 

src/message/header/mod.rs

@@ -7,7 +7,7 @@ use std::{
     ops::Deref,
 };
 
-use email_encoding::headers::EmailWriter;
+use email_encoding::headers::writer::EmailWriter;
 
 pub use self::{
     content::*,
@@ -348,7 +348,7 @@ impl<'a> HeaderValueEncoder<'a> {
 
     fn new(name: &str, writer: &'a mut dyn Write) -> Self {
         let line_len = name.len() + ": ".len();
-        let writer = EmailWriter::new(writer, line_len, 0, false, false);
+        let writer = EmailWriter::new(writer, line_len, 0, false);
 
         Self {
             writer,
@@ -612,17 +612,14 @@ mod tests {
             "🌍 <world@example.com>, 🦆 Everywhere <ducks@example.com>, Иванов Иван Иванович <ivanov@example.com>, Jānis Bērziņš <janis@example.com>, Seán Ó Rudaí <sean@example.com>".to_owned(),
         ));
 
-        // TODO: fix the fact that the encoder doesn't know that
-        // the space between the name and the address should be
-        // removed when wrapping.
         assert_eq!(
             headers.to_string(),
             concat!(
                 "To: =?utf-8?b?8J+MjQ==?= <world@example.com>, =?utf-8?b?8J+mhg==?=\r\n",
                 " Everywhere <ducks@example.com>, =?utf-8?b?0JjQstCw0L3QvtCyINCY0LLQsNC9?=\r\n",
                 " =?utf-8?b?INCY0LLQsNC90L7QstC40Yc=?= <ivanov@example.com>,\r\n",
-                "  =?utf-8?b?SsSBbmlzIELEk3J6acWGxaE=?= <janis@example.com>,\r\n",
-                "  =?utf-8?b?U2XDoW4gw5MgUnVkYcOt?= <sean@example.com>\r\n",
+                " =?utf-8?b?SsSBbmlzIELEk3J6acWGxaE=?= <janis@example.com>, =?utf-8?b?U2U=?=\r\n",
+                " =?utf-8?b?w6FuIMOTIFJ1ZGHDrQ==?= <sean@example.com>\r\n",
             )
         );
     }
@@ -687,9 +684,6 @@ mod tests {
             "quoted-printable".to_owned(),
         ));
 
-        // TODO: fix the fact that the encoder doesn't know that
-        // the space between the name and the address should be
-        // removed when wrapping.
         assert_eq!(
             headers.to_string(),
             concat!(
@@ -699,8 +693,8 @@ mod tests {
                 "To: =?utf-8?b?8J+MjQ==?= <world@example.com>, =?utf-8?b?8J+mhg==?=\r\n",
                 " Everywhere <ducks@example.com>, =?utf-8?b?0JjQstCw0L3QvtCyINCY0LLQsNC9?=\r\n",
                 " =?utf-8?b?INCY0LLQsNC90L7QstC40Yc=?= <ivanov@example.com>,\r\n",
-                "  =?utf-8?b?SsSBbmlzIELEk3J6acWGxaE=?= <janis@example.com>,\r\n",
-                "  =?utf-8?b?U2XDoW4gw5MgUnVkYcOt?= <sean@example.com>\r\n",
+                " =?utf-8?b?SsSBbmlzIELEk3J6acWGxaE=?= <janis@example.com>, =?utf-8?b?U2U=?=\r\n",
+                " =?utf-8?b?w6FuIMOTIFJ1ZGHDrQ==?= <sean@example.com>\r\n",
                 "From: Someone <somewhere@example.com>\r\n",
                 "Content-Transfer-Encoding: quoted-printable\r\n",
             )

src/message/mailbox/types.rs

@@ -6,7 +6,7 @@ use std::{
 };
 
 use chumsky::prelude::*;
-use email_encoding::headers::EmailWriter;
+use email_encoding::headers::writer::EmailWriter;
 
 use super::parsers;
 use crate::address::{Address, AddressError};
@@ -72,7 +72,7 @@ impl Mailbox {
     pub(crate) fn encode(&self, w: &mut EmailWriter<'_>) -> FmtResult {
         if let Some(name) = &self.name {
             email_encoding::headers::quoted_string::encode(name, w)?;
-            w.optional_breakpoint();
+            w.space();
             w.write_char('<')?;
         }
 
@@ -88,7 +88,7 @@ impl Mailbox {
 
 impl Display for Mailbox {
     fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
-        if let Some(ref name) = self.name {
+        if let Some(name) = &self.name {
             let name = name.trim();
             if !name.is_empty() {
                 write_word(f, name)?;
@@ -261,7 +261,7 @@ impl Mailboxes {
         for mailbox in self.iter() {
             if !mem::take(&mut first) {
                 w.write_char(',')?;
-                w.optional_breakpoint();
+                w.space();
             }
 
             mailbox.encode(w)?;
@@ -444,8 +444,6 @@ fn write_quoted_string_char(f: &mut Formatter<'_>, c: char) -> FmtResult {
 
 #[cfg(test)]
 mod test {
-    use std::convert::TryInto;
-
     use pretty_assertions::assert_eq;
 
     use super::Mailbox;

src/message/mimebody.rs

@@ -420,7 +420,6 @@ mod test {
     use pretty_assertions::assert_eq;
 
     use super::*;
-    use crate::message::header;
 
     #[test]
     fn single_part_binary() {

src/transport/file/error.rs

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

src/transport/mod.rs

@@ -32,7 +32,7 @@
 //! | [`smtp`]     | SMTP     | [`SmtpTransport`]     | [`AsyncSmtpTransport`]     | Uses the SMTP protocol to send emails to a relay server |
 //! | [`sendmail`] | Sendmail | [`SendmailTransport`] | [`AsyncSendmailTransport`] | Uses the `sendmail` command to send emails              |
 //! | [`file`]     | File     | [`FileTransport`]     | [`AsyncFileTransport`]     | Saves the email as an `.eml` file                       |
-//! | [`stub`]     | Debug    | [`StubTransport`]     | [`StubTransport`]          | Drops the email - Useful for debugging                  |
+//! | [`stub`]     | Debug    | [`StubTransport`]     | [`AsyncStubTransport`]     | Drops the email - Useful for debugging                  |
 //!
 //! ## Building an email
 //!
@@ -97,6 +97,7 @@
 //! [`FileTransport`]: crate::FileTransport
 //! [`AsyncFileTransport`]: crate::AsyncFileTransport
 //! [`StubTransport`]: crate::transport::stub::StubTransport
+//! [`AsyncStubTransport`]: crate::transport::stub::AsyncStubTransport
 
 #[cfg(any(feature = "async-std1", feature = "tokio1"))]
 use async_trait::async_trait;

src/transport/sendmail/error.rs

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

src/transport/smtp/authentication.rs

@@ -98,11 +98,13 @@ impl Mechanism {
                 let decoded_challenge = challenge
                     .ok_or_else(|| error::client("This mechanism does expect a challenge"))?;
 
-                if ["User Name", "Username:", "Username"].contains(&decoded_challenge) {
+                if ["User Name", "Username:", "Username", "User Name\0"]
+                    .contains(&decoded_challenge)
+                {
                     return Ok(credentials.authentication_identity.clone());
                 }
 
-                if ["Password", "Password:"].contains(&decoded_challenge) {
+                if ["Password", "Password:", "Password\0"].contains(&decoded_challenge) {
                     return Ok(credentials.secret.clone());
                 }
 

src/transport/smtp/client/async_connection.rs

@@ -65,7 +65,7 @@ impl AsyncSmtpConnection {
     /// If `tls_parameters` is `Some`, then the connection will use Implicit TLS (sometimes
     /// referred to as `SMTPS`). See also [`AsyncSmtpConnection::starttls`].
     ///
-    /// If `local_addres` is `Some`, then the address provided shall be used to bind the
+    /// If `local_address` is `Some`, then the address provided shall be used to bind the
     /// connection to a specific local address using [`tokio1_crate::net::TcpSocket::bind`].
     ///
     /// Sends EHLO and parses server information

src/transport/smtp/client/async_net.rs

@@ -106,23 +106,23 @@ impl AsyncNetworkStream {
 
     /// Returns peer's address
     pub fn peer_addr(&self) -> IoResult<SocketAddr> {
-        match self.inner {
+        match &self.inner {
             #[cfg(feature = "tokio1")]
-            InnerAsyncNetworkStream::Tokio1Tcp(ref s) => s.peer_addr(),
+            InnerAsyncNetworkStream::Tokio1Tcp(s) => s.peer_addr(),
             #[cfg(feature = "tokio1-native-tls")]
-            InnerAsyncNetworkStream::Tokio1NativeTls(ref s) => {
+            InnerAsyncNetworkStream::Tokio1NativeTls(s) => {
                 s.get_ref().get_ref().get_ref().peer_addr()
             }
             #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(ref s) => s.get_ref().0.peer_addr(),
+            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => s.get_ref().0.peer_addr(),
             #[cfg(feature = "tokio1-boring-tls")]
-            InnerAsyncNetworkStream::Tokio1BoringTls(ref s) => s.get_ref().peer_addr(),
+            InnerAsyncNetworkStream::Tokio1BoringTls(s) => s.get_ref().peer_addr(),
             #[cfg(feature = "async-std1")]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(ref s) => s.peer_addr(),
+            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => s.peer_addr(),
             #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(ref s) => s.get_ref().peer_addr(),
+            InnerAsyncNetworkStream::AsyncStd1NativeTls(s) => s.get_ref().peer_addr(),
             #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(ref s) => s.get_ref().0.peer_addr(),
+            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => s.get_ref().0.peer_addr(),
             InnerAsyncNetworkStream::None => {
                 debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
                 Err(IoError::new(
@@ -445,7 +445,7 @@ impl AsyncNetworkStream {
     }
 
     pub fn is_encrypted(&self) -> bool {
-        match self.inner {
+        match &self.inner {
             #[cfg(feature = "tokio1")]
             InnerAsyncNetworkStream::Tokio1Tcp(_) => false,
             #[cfg(feature = "tokio1-native-tls")]
@@ -520,9 +520,9 @@ impl FuturesAsyncRead for AsyncNetworkStream {
         cx: &mut Context<'_>,
         buf: &mut [u8],
     ) -> Poll<IoResult<usize>> {
-        match self.inner {
+        match &mut self.inner {
             #[cfg(feature = "tokio1")]
-            InnerAsyncNetworkStream::Tokio1Tcp(ref mut s) => {
+            InnerAsyncNetworkStream::Tokio1Tcp(s) => {
                 let mut b = Tokio1ReadBuf::new(buf);
                 match Pin::new(s).poll_read(cx, &mut b) {
                     Poll::Ready(Ok(())) => Poll::Ready(Ok(b.filled().len())),
@@ -531,7 +531,7 @@ impl FuturesAsyncRead for AsyncNetworkStream {
                 }
             }
             #[cfg(feature = "tokio1-native-tls")]
-            InnerAsyncNetworkStream::Tokio1NativeTls(ref mut s) => {
+            InnerAsyncNetworkStream::Tokio1NativeTls(s) => {
                 let mut b = Tokio1ReadBuf::new(buf);
                 match Pin::new(s).poll_read(cx, &mut b) {
                     Poll::Ready(Ok(())) => Poll::Ready(Ok(b.filled().len())),
@@ -540,7 +540,7 @@ impl FuturesAsyncRead for AsyncNetworkStream {
                 }
             }
             #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(ref mut s) => {
+            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => {
                 let mut b = Tokio1ReadBuf::new(buf);
                 match Pin::new(s).poll_read(cx, &mut b) {
                     Poll::Ready(Ok(())) => Poll::Ready(Ok(b.filled().len())),
@@ -549,7 +549,7 @@ impl FuturesAsyncRead for AsyncNetworkStream {
                 }
             }
             #[cfg(feature = "tokio1-boring-tls")]
-            InnerAsyncNetworkStream::Tokio1BoringTls(ref mut s) => {
+            InnerAsyncNetworkStream::Tokio1BoringTls(s) => {
                 let mut b = Tokio1ReadBuf::new(buf);
                 match Pin::new(s).poll_read(cx, &mut b) {
                     Poll::Ready(Ok(())) => Poll::Ready(Ok(b.filled().len())),
@@ -558,15 +558,11 @@ impl FuturesAsyncRead for AsyncNetworkStream {
                 }
             }
             #[cfg(feature = "async-std1")]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(ref mut s) => Pin::new(s).poll_read(cx, buf),
+            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => Pin::new(s).poll_read(cx, buf),
             #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(ref mut s) => {
-                Pin::new(s).poll_read(cx, buf)
-            }
+            InnerAsyncNetworkStream::AsyncStd1NativeTls(s) => Pin::new(s).poll_read(cx, buf),
             #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(ref mut s) => {
-                Pin::new(s).poll_read(cx, buf)
-            }
+            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => Pin::new(s).poll_read(cx, buf),
             InnerAsyncNetworkStream::None => {
                 debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
                 Poll::Ready(Ok(0))
@@ -581,25 +577,21 @@ impl FuturesAsyncWrite for AsyncNetworkStream {
         cx: &mut Context<'_>,
         buf: &[u8],
     ) -> Poll<IoResult<usize>> {
-        match self.inner {
+        match &mut self.inner {
             #[cfg(feature = "tokio1")]
-            InnerAsyncNetworkStream::Tokio1Tcp(ref mut s) => Pin::new(s).poll_write(cx, buf),
+            InnerAsyncNetworkStream::Tokio1Tcp(s) => Pin::new(s).poll_write(cx, buf),
             #[cfg(feature = "tokio1-native-tls")]
-            InnerAsyncNetworkStream::Tokio1NativeTls(ref mut s) => Pin::new(s).poll_write(cx, buf),
+            InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_write(cx, buf),
             #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(ref mut s) => Pin::new(s).poll_write(cx, buf),
+            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => Pin::new(s).poll_write(cx, buf),
             #[cfg(feature = "tokio1-boring-tls")]
-            InnerAsyncNetworkStream::Tokio1BoringTls(ref mut s) => Pin::new(s).poll_write(cx, buf),
+            InnerAsyncNetworkStream::Tokio1BoringTls(s) => Pin::new(s).poll_write(cx, buf),
             #[cfg(feature = "async-std1")]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(ref mut s) => Pin::new(s).poll_write(cx, buf),
+            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => Pin::new(s).poll_write(cx, buf),
             #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(ref mut s) => {
-                Pin::new(s).poll_write(cx, buf)
-            }
+            InnerAsyncNetworkStream::AsyncStd1NativeTls(s) => Pin::new(s).poll_write(cx, buf),
             #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(ref mut s) => {
-                Pin::new(s).poll_write(cx, buf)
-            }
+            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => Pin::new(s).poll_write(cx, buf),
             InnerAsyncNetworkStream::None => {
                 debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
                 Poll::Ready(Ok(0))
@@ -608,21 +600,21 @@ impl FuturesAsyncWrite for AsyncNetworkStream {
     }
 
     fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<IoResult<()>> {
-        match self.inner {
+        match &mut self.inner {
             #[cfg(feature = "tokio1")]
-            InnerAsyncNetworkStream::Tokio1Tcp(ref mut s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::Tokio1Tcp(s) => Pin::new(s).poll_flush(cx),
             #[cfg(feature = "tokio1-native-tls")]
-            InnerAsyncNetworkStream::Tokio1NativeTls(ref mut s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_flush(cx),
             #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(ref mut s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => Pin::new(s).poll_flush(cx),
             #[cfg(feature = "tokio1-boring-tls")]
-            InnerAsyncNetworkStream::Tokio1BoringTls(ref mut s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::Tokio1BoringTls(s) => Pin::new(s).poll_flush(cx),
             #[cfg(feature = "async-std1")]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(ref mut s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => Pin::new(s).poll_flush(cx),
             #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(ref mut s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::AsyncStd1NativeTls(s) => Pin::new(s).poll_flush(cx),
             #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(ref mut s) => Pin::new(s).poll_flush(cx),
+            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => Pin::new(s).poll_flush(cx),
             InnerAsyncNetworkStream::None => {
                 debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
                 Poll::Ready(Ok(()))
@@ -631,21 +623,21 @@ impl FuturesAsyncWrite for AsyncNetworkStream {
     }
 
     fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<IoResult<()>> {
-        match self.inner {
+        match &mut self.inner {
             #[cfg(feature = "tokio1")]
-            InnerAsyncNetworkStream::Tokio1Tcp(ref mut s) => Pin::new(s).poll_shutdown(cx),
+            InnerAsyncNetworkStream::Tokio1Tcp(s) => Pin::new(s).poll_shutdown(cx),
             #[cfg(feature = "tokio1-native-tls")]
-            InnerAsyncNetworkStream::Tokio1NativeTls(ref mut s) => Pin::new(s).poll_shutdown(cx),
+            InnerAsyncNetworkStream::Tokio1NativeTls(s) => Pin::new(s).poll_shutdown(cx),
             #[cfg(feature = "tokio1-rustls-tls")]
-            InnerAsyncNetworkStream::Tokio1RustlsTls(ref mut s) => Pin::new(s).poll_shutdown(cx),
+            InnerAsyncNetworkStream::Tokio1RustlsTls(s) => Pin::new(s).poll_shutdown(cx),
             #[cfg(feature = "tokio1-boring-tls")]
-            InnerAsyncNetworkStream::Tokio1BoringTls(ref mut s) => Pin::new(s).poll_shutdown(cx),
+            InnerAsyncNetworkStream::Tokio1BoringTls(s) => Pin::new(s).poll_shutdown(cx),
             #[cfg(feature = "async-std1")]
-            InnerAsyncNetworkStream::AsyncStd1Tcp(ref mut s) => Pin::new(s).poll_close(cx),
+            InnerAsyncNetworkStream::AsyncStd1Tcp(s) => Pin::new(s).poll_close(cx),
             #[cfg(feature = "async-std1-native-tls")]
-            InnerAsyncNetworkStream::AsyncStd1NativeTls(ref mut s) => Pin::new(s).poll_close(cx),
+            InnerAsyncNetworkStream::AsyncStd1NativeTls(s) => Pin::new(s).poll_close(cx),
             #[cfg(feature = "async-std1-rustls-tls")]
-            InnerAsyncNetworkStream::AsyncStd1RustlsTls(ref mut s) => Pin::new(s).poll_close(cx),
+            InnerAsyncNetworkStream::AsyncStd1RustlsTls(s) => Pin::new(s).poll_close(cx),
             InnerAsyncNetworkStream::None => {
                 debug_assert!(false, "InnerAsyncNetworkStream::None must never be built");
                 Poll::Ready(Ok(()))

src/transport/smtp/client/net.rs

@@ -55,14 +55,14 @@ impl NetworkStream {
 
     /// Returns peer's address
     pub fn peer_addr(&self) -> io::Result<SocketAddr> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref s) => s.peer_addr(),
+        match &self.inner {
+            InnerNetworkStream::Tcp(s) => s.peer_addr(),
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref s) => s.get_ref().peer_addr(),
+            InnerNetworkStream::NativeTls(s) => s.get_ref().peer_addr(),
             #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref s) => s.get_ref().peer_addr(),
+            InnerNetworkStream::RustlsTls(s) => s.get_ref().peer_addr(),
             #[cfg(feature = "boring-tls")]
-            InnerNetworkStream::BoringTls(ref s) => s.get_ref().peer_addr(),
+            InnerNetworkStream::BoringTls(s) => s.get_ref().peer_addr(),
             InnerNetworkStream::None => {
                 debug_assert!(false, "InnerNetworkStream::None must never be built");
                 Ok(SocketAddr::V4(SocketAddrV4::new(
@@ -75,14 +75,14 @@ impl NetworkStream {
 
     /// Shutdowns the connection
     pub fn shutdown(&self, how: Shutdown) -> io::Result<()> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref s) => s.shutdown(how),
+        match &self.inner {
+            InnerNetworkStream::Tcp(s) => s.shutdown(how),
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref s) => s.get_ref().shutdown(how),
+            InnerNetworkStream::NativeTls(s) => s.get_ref().shutdown(how),
             #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref s) => s.get_ref().shutdown(how),
+            InnerNetworkStream::RustlsTls(s) => s.get_ref().shutdown(how),
             #[cfg(feature = "boring-tls")]
-            InnerNetworkStream::BoringTls(ref s) => s.get_ref().shutdown(how),
+            InnerNetworkStream::BoringTls(s) => s.get_ref().shutdown(how),
             InnerNetworkStream::None => {
                 debug_assert!(false, "InnerNetworkStream::None must never be built");
                 Ok(())
@@ -208,7 +208,7 @@ impl NetworkStream {
     }
 
     pub fn is_encrypted(&self) -> bool {
-        match self.inner {
+        match &self.inner {
             InnerNetworkStream::Tcp(_) => false,
             #[cfg(feature = "native-tls")]
             InnerNetworkStream::NativeTls(_) => true,
@@ -254,20 +254,14 @@ impl NetworkStream {
     }
 
     pub fn set_read_timeout(&mut self, duration: Option<Duration>) -> io::Result<()> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref mut stream) => stream.set_read_timeout(duration),
+        match &mut self.inner {
+            InnerNetworkStream::Tcp(stream) => stream.set_read_timeout(duration),
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref mut stream) => {
-                stream.get_ref().set_read_timeout(duration)
-            }
+            InnerNetworkStream::NativeTls(stream) => stream.get_ref().set_read_timeout(duration),
             #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut stream) => {
-                stream.get_ref().set_read_timeout(duration)
-            }
+            InnerNetworkStream::RustlsTls(stream) => stream.get_ref().set_read_timeout(duration),
             #[cfg(feature = "boring-tls")]
-            InnerNetworkStream::BoringTls(ref mut stream) => {
-                stream.get_ref().set_read_timeout(duration)
-            }
+            InnerNetworkStream::BoringTls(stream) => stream.get_ref().set_read_timeout(duration),
             InnerNetworkStream::None => {
                 debug_assert!(false, "InnerNetworkStream::None must never be built");
                 Ok(())
@@ -277,21 +271,15 @@ impl NetworkStream {
 
     /// Set write timeout for IO calls
     pub fn set_write_timeout(&mut self, duration: Option<Duration>) -> io::Result<()> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref mut stream) => stream.set_write_timeout(duration),
+        match &mut self.inner {
+            InnerNetworkStream::Tcp(stream) => stream.set_write_timeout(duration),
 
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref mut stream) => {
-                stream.get_ref().set_write_timeout(duration)
-            }
+            InnerNetworkStream::NativeTls(stream) => stream.get_ref().set_write_timeout(duration),
             #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut stream) => {
-                stream.get_ref().set_write_timeout(duration)
-            }
+            InnerNetworkStream::RustlsTls(stream) => stream.get_ref().set_write_timeout(duration),
             #[cfg(feature = "boring-tls")]
-            InnerNetworkStream::BoringTls(ref mut stream) => {
-                stream.get_ref().set_write_timeout(duration)
-            }
+            InnerNetworkStream::BoringTls(stream) => stream.get_ref().set_write_timeout(duration),
             InnerNetworkStream::None => {
                 debug_assert!(false, "InnerNetworkStream::None must never be built");
                 Ok(())
@@ -302,14 +290,14 @@ impl NetworkStream {
 
 impl Read for NetworkStream {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref mut s) => s.read(buf),
+        match &mut self.inner {
+            InnerNetworkStream::Tcp(s) => s.read(buf),
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref mut s) => s.read(buf),
+            InnerNetworkStream::NativeTls(s) => s.read(buf),
             #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut s) => s.read(buf),
+            InnerNetworkStream::RustlsTls(s) => s.read(buf),
             #[cfg(feature = "boring-tls")]
-            InnerNetworkStream::BoringTls(ref mut s) => s.read(buf),
+            InnerNetworkStream::BoringTls(s) => s.read(buf),
             InnerNetworkStream::None => {
                 debug_assert!(false, "InnerNetworkStream::None must never be built");
                 Ok(0)
@@ -320,14 +308,14 @@ impl Read for NetworkStream {
 
 impl Write for NetworkStream {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref mut s) => s.write(buf),
+        match &mut self.inner {
+            InnerNetworkStream::Tcp(s) => s.write(buf),
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref mut s) => s.write(buf),
+            InnerNetworkStream::NativeTls(s) => s.write(buf),
             #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut s) => s.write(buf),
+            InnerNetworkStream::RustlsTls(s) => s.write(buf),
             #[cfg(feature = "boring-tls")]
-            InnerNetworkStream::BoringTls(ref mut s) => s.write(buf),
+            InnerNetworkStream::BoringTls(s) => s.write(buf),
             InnerNetworkStream::None => {
                 debug_assert!(false, "InnerNetworkStream::None must never be built");
                 Ok(0)
@@ -336,14 +324,14 @@ impl Write for NetworkStream {
     }
 
     fn flush(&mut self) -> io::Result<()> {
-        match self.inner {
-            InnerNetworkStream::Tcp(ref mut s) => s.flush(),
+        match &mut self.inner {
+            InnerNetworkStream::Tcp(s) => s.flush(),
             #[cfg(feature = "native-tls")]
-            InnerNetworkStream::NativeTls(ref mut s) => s.flush(),
+            InnerNetworkStream::NativeTls(s) => s.flush(),
             #[cfg(feature = "rustls-tls")]
-            InnerNetworkStream::RustlsTls(ref mut s) => s.flush(),
+            InnerNetworkStream::RustlsTls(s) => s.flush(),
             #[cfg(feature = "boring-tls")]
-            InnerNetworkStream::BoringTls(ref mut s) => s.flush(),
+            InnerNetworkStream::BoringTls(s) => s.flush(),
             InnerNetworkStream::None => {
                 debug_assert!(false, "InnerNetworkStream::None must never be built");
                 Ok(())

src/transport/smtp/error.rs

@@ -119,7 +119,7 @@ impl fmt::Debug for Error {
 
         builder.field("kind", &self.inner.kind);
 
-        if let Some(ref source) = self.inner.source {
+        if let Some(source) = &self.inner.source {
             builder.field("source", source);
         }
 
@@ -129,22 +129,22 @@ impl fmt::Debug for Error {
 
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self.inner.kind {
+        match &self.inner.kind {
             Kind::Response => f.write_str("response error")?,
             Kind::Client => f.write_str("internal client error")?,
             Kind::Network => f.write_str("network error")?,
             Kind::Connection => f.write_str("Connection error")?,
             #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
             Kind::Tls => f.write_str("tls error")?,
-            Kind::Transient(ref code) => {
+            Kind::Transient(code) => {
                 write!(f, "transient error ({code})")?;
             }
-            Kind::Permanent(ref code) => {
+            Kind::Permanent(code) => {
                 write!(f, "permanent error ({code})")?;
             }
         };
 
-        if let Some(ref e) = self.inner.source {
+        if let Some(e) = &self.inner.source {
             write!(f, ": {e}")?;
         }
 

src/transport/smtp/extension.rs

@@ -4,7 +4,6 @@ use std::{
     collections::HashSet,
     fmt::{self, Display, Formatter},
     net::{Ipv4Addr, Ipv6Addr},
-    result::Result,
 };
 
 use crate::transport::smtp::{
@@ -53,10 +52,10 @@ impl Default for ClientId {
 
 impl Display for ClientId {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        match *self {
-            Self::Domain(ref value) => f.write_str(value),
-            Self::Ipv4(ref value) => write!(f, "[{value}]"),
-            Self::Ipv6(ref value) => write!(f, "[IPv6:{value}]"),
+        match self {
+            Self::Domain(value) => f.write_str(value),
+            Self::Ipv4(value) => write!(f, "[{value}]"),
+            Self::Ipv6(value) => write!(f, "[IPv6:{value}]"),
         }
     }
 }
@@ -93,11 +92,11 @@ pub enum Extension {
 
 impl Display for Extension {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        match *self {
+        match self {
             Extension::EightBitMime => f.write_str("8BITMIME"),
             Extension::SmtpUtfEight => f.write_str("SMTPUTF8"),
             Extension::StartTls => f.write_str("STARTTLS"),
-            Extension::Authentication(ref mechanism) => write!(f, "AUTH {mechanism}"),
+            Extension::Authentication(mechanism) => write!(f, "AUTH {mechanism}"),
         }
     }
 }
@@ -227,16 +226,16 @@ pub enum MailParameter {
 
 impl Display for MailParameter {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        match *self {
-            MailParameter::Body(ref value) => write!(f, "BODY={value}"),
+        match self {
+            MailParameter::Body(value) => write!(f, "BODY={value}"),
             MailParameter::Size(size) => write!(f, "SIZE={size}"),
             MailParameter::SmtpUtfEight => f.write_str("SMTPUTF8"),
             MailParameter::Other {
-                ref keyword,
-                value: Some(ref value),
+                keyword,
+                value: Some(value),
             } => write!(f, "{}={}", keyword, XText(value)),
             MailParameter::Other {
-                ref keyword,
+                keyword,
                 value: None,
             } => f.write_str(keyword),
         }
@@ -277,13 +276,13 @@ pub enum RcptParameter {
 
 impl Display for RcptParameter {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        match *self {
+        match &self {
             RcptParameter::Other {
-                ref keyword,
-                value: Some(ref value),
+                keyword,
+                value: Some(value),
             } => write!(f, "{keyword}={}", XText(value)),
             RcptParameter::Other {
-                ref keyword,
+                keyword,
                 value: None,
             } => f.write_str(keyword),
         }
@@ -292,14 +291,8 @@ impl Display for RcptParameter {
 
 #[cfg(test)]
 mod test {
-
-    use std::collections::HashSet;
-
     use super::*;
-    use crate::transport::smtp::{
-        authentication::Mechanism,
-        response::{Category, Code, Detail, Response, Severity},
-    };
+    use crate::transport::smtp::response::{Category, Code, Detail, Severity};
 
     #[test]
     fn test_clientid_fmt() {

src/transport/smtp/response.rs

@@ -5,7 +5,6 @@ use std::{
     fmt::{Display, Formatter, Result},
     result,
     str::FromStr,
-    string::ToString,
 };
 
 use nom::{
@@ -132,6 +131,12 @@ impl Code {
     }
 }
 
+impl From<Code> for u16 {
+    fn from(code: Code) -> Self {
+        code.detail as u16 + 10 * code.category as u16 + 100 * code.severity as u16
+    }
+}
+
 /// Contains an SMTP reply, with separated code and message
 ///
 /// The text message is optional, only the code is mandatory
@@ -317,6 +322,17 @@ mod test {
         assert_eq!(code.to_string(), "421");
     }
 
+    #[test]
+    fn test_code_to_u16() {
+        let code = Code {
+            severity: Severity::TransientNegativeCompletion,
+            category: Category::Connections,
+            detail: Detail::One,
+        };
+        let c: u16 = code.into();
+        assert_eq!(c, 421);
+    }
+
     #[test]
     fn test_response_from_str() {
         let raw_response = "250-me\r\n250-8BITMIME\r\n250-SIZE 42\r\n250 AUTH PLAIN CRAM-MD5\r\n";

src/transport/smtp/transport.rs

@@ -317,9 +317,9 @@ impl SmtpClient {
     /// Handles encryption and authentication
     pub fn connection(&self) -> Result<SmtpConnection, Error> {
         #[allow(clippy::match_single_binding)]
-        let tls_parameters = match self.info.tls {
+        let tls_parameters = match &self.info.tls {
             #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
-            Tls::Wrapper(ref tls_parameters) => Some(tls_parameters),
+            Tls::Wrapper(tls_parameters) => Some(tls_parameters),
             _ => None,
         };
 
@@ -333,13 +333,13 @@ impl SmtpClient {
         )?;
 
         #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
-        match self.info.tls {
-            Tls::Opportunistic(ref tls_parameters) => {
+        match &self.info.tls {
+            Tls::Opportunistic(tls_parameters) => {
                 if conn.can_starttls() {
                     conn.starttls(tls_parameters, &self.info.hello_name)?;
                 }
             }
-            Tls::Required(ref tls_parameters) => {
+            Tls::Required(tls_parameters) => {
                 conn.starttls(tls_parameters, &self.info.hello_name)?;
             }
             _ => (),