Prepare 0.10.4 (#871)

.github/workflows/test.yml

@@ -122,10 +122,10 @@ jobs:
         run: cargo test
 
       - name: Test with all features (-native-tls)
-        run: cargo test --no-default-features --features async-std,async-std1,async-std1-rustls-tls,async-trait,base64,boring,boring-tls,builder,dkim,ed25519-dalek,email-encoding,fastrand,file-transport,file-transport-envelope,futures-io,futures-rustls,futures-util,hostname,httpdate,mime,mime03,nom,once_cell,pool,quoted_printable,rsa,rustls,rustls-pemfile,rustls-tls,sendmail-transport,serde,serde_json,sha2,smtp-transport,socket2,tokio1,tokio1-boring-tls,tokio1-rustls-tls,tokio1_boring,tokio1_crate,tokio1_rustls,tracing,uuid,webpki-roots
+        run: cargo test --no-default-features --features async-std,async-std1,async-std1-rustls-tls,async-trait,base64,boring,boring-tls,builder,dkim,ed25519-dalek,email-encoding,fastrand,file-transport,file-transport-envelope,futures-io,futures-rustls,futures-util,hostname,httpdate,mime,mime03,nom,once_cell,pool,quoted_printable,rsa,rustls,rustls-native-certs,rustls-pemfile,rustls-tls,sendmail-transport,serde,serde_json,sha2,smtp-transport,socket2,tokio1,tokio1-boring-tls,tokio1-rustls-tls,tokio1_boring,tokio1_crate,tokio1_rustls,tracing,uuid,webpki-roots
   
       - name: Test with all features (-boring-tls)
-        run: cargo test --no-default-features --features async-std,async-std1,async-std1-rustls-tls,async-trait,base64,builder,dkim,ed25519-dalek,email-encoding,fastrand,file-transport,file-transport-envelope,futures-io,futures-rustls,futures-util,hostname,httpdate,mime,mime03,native-tls,nom,once_cell,pool,quoted_printable,rsa,rustls,rustls-pemfile,rustls-tls,sendmail-transport,serde,serde_json,sha2,smtp-transport,socket2,tokio1,tokio1-native-tls,tokio1-rustls-tls,tokio1_crate,tokio1_native_tls_crate,tokio1_rustls,tracing,uuid,webpki-roots
+        run: cargo test --no-default-features --features async-std,async-std1,async-std1-rustls-tls,async-trait,base64,builder,dkim,ed25519-dalek,email-encoding,fastrand,file-transport,file-transport-envelope,futures-io,futures-rustls,futures-util,hostname,httpdate,mime,mime03,native-tls,nom,once_cell,pool,quoted_printable,rsa,rustls,rustls-native-certs,rustls-pemfile,rustls-tls,sendmail-transport,serde,serde_json,sha2,smtp-transport,socket2,tokio1,tokio1-native-tls,tokio1-rustls-tls,tokio1_crate,tokio1_native_tls_crate,tokio1_rustls,tracing,uuid,webpki-roots
 
 #  coverage:
 #    name: Coverage

CHANGELOG.md

@@ -1,3 +1,45 @@
+<a name="v0.10.4"></a>
+### v0.10.4 (2023-04-02)
+
+#### Misc
+
+* Bumped rustls to 0.21 and all related dependencies ([#867])
+
+[#867]: https://github.com/lettre/lettre/pull/867
+
+<a name="v0.10.3"></a>
+### v0.10.3 (2023-02-20)
+
+#### Announcements
+
+It was found that what had been used until now as a basic lettre 0.10
+`MessageBuilder::body` example failed to mention that for maximum
+compatibility with various email clients a `Content-Type` header
+should always be present in the message.
+
+##### Before
+
+```rust
+Message::builder()
+  // [...] some headers skipped for brevity
+  .body(String::from("A plaintext or html body"))?
+```
+
+##### Patch
+
+```diff
+ Message::builder()
+   // [...] some headers skipped for brevity
++  .header(ContentType::TEXT_PLAIN) // or `TEXT_HTML` if the body is html
+   .body(String::from("A plaintext or html body"))?
+```
+
+#### Features
+
+* Add support for rustls-native-certs when using rustls ([#843])
+
+[#843]: https://github.com/lettre/lettre/pull/843
+
 <a name="v0.10.2"></a>
 ### v0.10.2 (2023-01-29)
 

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "lettre"
 # remember to update html_root_url and README.md (Cargo.toml example and deps.rs badge)
-version = "0.10.2"
+version = "0.10.4"
 description = "Email client"
 readme = "README.md"
 homepage = "https://lettre.rs"
@@ -43,9 +43,10 @@ socket2 = { version = "0.4.4", optional = true }
 
 ## tls
 native-tls = { version = "0.2", optional = true } # feature
-rustls = { version = "0.20", features = ["dangerous_configuration"], optional = true }
+rustls = { version = "0.21", features = ["dangerous_configuration"], optional = true }
 rustls-pemfile = { version = "1", optional = true }
-webpki-roots = { version = "0.22", optional = true }
+rustls-native-certs = { version = "0.6.2", optional = true }
+webpki-roots = { version = "0.23", optional = true }
 boring = { version = "2.0.0", optional = true }
 
 # async
@@ -56,12 +57,12 @@ 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 = "0.22", optional = true }
+futures-rustls = { version = "0.24", optional = true }
 
 ## tokio
 tokio1_crate = { package = "tokio", version = "1", optional = true }
 tokio1_native_tls_crate = { package = "tokio-native-tls", version = "0.3", optional = true }
-tokio1_rustls = { package = "tokio-rustls", version = "0.23", optional = true }
+tokio1_rustls = { package = "tokio-rustls", version = "0.24", optional = true }
 tokio1_boring = { package = "tokio-boring", version = "2.1.4", optional = true }
 
 ## dkim

README.md

@@ -28,8 +28,8 @@
 </div>
 
 <div align="center">
-  <a href="https://deps.rs/crate/lettre/0.10.2">
-    <img src="https://deps.rs/crate/lettre/0.10.2/status.svg"
+  <a href="https://deps.rs/crate/lettre/0.10.4">
+    <img src="https://deps.rs/crate/lettre/0.10.4/status.svg"
       alt="dependency status" />
   </a>
 </div>
@@ -67,6 +67,7 @@ lettre = "0.10"
 ```
 
 ```rust,no_run
+use lettre::message::header::ContentType;
 use lettre::transport::smtp::authentication::Credentials;
 use lettre::{Message, SmtpTransport, Transport};
 
@@ -75,10 +76,11 @@ let email = Message::builder()
     .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
     .to("Hei <hei@domain.tld>".parse().unwrap())
     .subject("Happy new year")
+    .header(ContentType::TEXT_PLAIN)
     .body(String::from("Be happy!"))
     .unwrap();
 
-let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
 // Open a remote connection to gmail
 let mailer = SmtpTransport::relay("smtp.gmail.com")

examples/asyncstd1_smtp_starttls.rs

@@ -1,6 +1,6 @@
 use lettre::{
-    transport::smtp::authentication::Credentials, AsyncSmtpTransport, AsyncStd1Executor,
-    AsyncTransport, Message,
+    message::header::ContentType, transport::smtp::authentication::Credentials, AsyncSmtpTransport,
+    AsyncStd1Executor, AsyncTransport, Message,
 };
 
 #[async_std::main]
@@ -12,10 +12,11 @@ async fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new async year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy with async!"))
         .unwrap();
 
-    let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+    let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
     // Open a remote connection to gmail using STARTTLS
     let mailer: AsyncSmtpTransport<AsyncStd1Executor> =

examples/asyncstd1_smtp_tls.rs

@@ -1,6 +1,6 @@
 use lettre::{
-    transport::smtp::authentication::Credentials, AsyncSmtpTransport, AsyncStd1Executor,
-    AsyncTransport, Message,
+    message::header::ContentType, transport::smtp::authentication::Credentials, AsyncSmtpTransport,
+    AsyncStd1Executor, AsyncTransport, Message,
 };
 
 #[async_std::main]
@@ -12,10 +12,11 @@ async fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new async year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy with async!"))
         .unwrap();
 
-    let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+    let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
     // Open a remote connection to gmail
     let mailer: AsyncSmtpTransport<AsyncStd1Executor> =

examples/smtp.rs

@@ -1,4 +1,4 @@
-use lettre::{Message, SmtpTransport, Transport};
+use lettre::{message::header::ContentType, Message, SmtpTransport, Transport};
 
 fn main() {
     tracing_subscriber::fmt::init();
@@ -8,6 +8,7 @@ fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy!"))
         .unwrap();
 

examples/smtp_selfsigned.rs

@@ -1,6 +1,7 @@
 use std::fs;
 
 use lettre::{
+    message::header::ContentType,
     transport::smtp::{
         authentication::Credentials,
         client::{Certificate, Tls, TlsParameters},
@@ -16,18 +17,19 @@ fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy!"))
         .unwrap();
 
     // Use a custom certificate stored on disk to securely verify the server's certificate
     let pem_cert = fs::read("certificate.pem").unwrap();
     let cert = Certificate::from_pem(&pem_cert).unwrap();
-    let tls = TlsParameters::builder("smtp.server.com".to_string())
+    let tls = TlsParameters::builder("smtp.server.com".to_owned())
         .add_root_certificate(cert)
         .build()
         .unwrap();
 
-    let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+    let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
     // Open a remote connection to the smtp server
     let mailer = SmtpTransport::builder_dangerous("smtp.server.com")

examples/smtp_starttls.rs

@@ -1,4 +1,7 @@
-use lettre::{transport::smtp::authentication::Credentials, Message, SmtpTransport, Transport};
+use lettre::{
+    message::header::ContentType, transport::smtp::authentication::Credentials, Message,
+    SmtpTransport, Transport,
+};
 
 fn main() {
     tracing_subscriber::fmt::init();
@@ -8,10 +11,11 @@ fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy!"))
         .unwrap();
 
-    let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+    let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
     // Open a remote connection to gmail using STARTTLS
     let mailer = SmtpTransport::starttls_relay("smtp.gmail.com")

examples/smtp_tls.rs

@@ -1,4 +1,7 @@
-use lettre::{transport::smtp::authentication::Credentials, Message, SmtpTransport, Transport};
+use lettre::{
+    message::header::ContentType, transport::smtp::authentication::Credentials, Message,
+    SmtpTransport, Transport,
+};
 
 fn main() {
     tracing_subscriber::fmt::init();
@@ -8,10 +11,11 @@ fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy!"))
         .unwrap();
 
-    let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+    let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
     // Open a remote connection to gmail
     let mailer = SmtpTransport::relay("smtp.gmail.com")

examples/tokio1_smtp_starttls.rs

@@ -2,8 +2,8 @@
 // since it uses Rust 2018 crate renaming to import tokio.
 // Won't be needed in user's code.
 use lettre::{
-    transport::smtp::authentication::Credentials, AsyncSmtpTransport, AsyncTransport, Message,
-    Tokio1Executor,
+    message::header::ContentType, transport::smtp::authentication::Credentials, AsyncSmtpTransport,
+    AsyncTransport, Message, Tokio1Executor,
 };
 use tokio1_crate as tokio;
 
@@ -16,10 +16,11 @@ async fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new async year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy with async!"))
         .unwrap();
 
-    let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+    let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
     // Open a remote connection to gmail using STARTTLS
     let mailer: AsyncSmtpTransport<Tokio1Executor> =

examples/tokio1_smtp_tls.rs

@@ -2,8 +2,8 @@
 // since it uses Rust 2018 crate renaming to import tokio.
 // Won't be needed in user's code.
 use lettre::{
-    transport::smtp::authentication::Credentials, AsyncSmtpTransport, AsyncTransport, Message,
-    Tokio1Executor,
+    message::header::ContentType, transport::smtp::authentication::Credentials, AsyncSmtpTransport,
+    AsyncTransport, Message, Tokio1Executor,
 };
 use tokio1_crate as tokio;
 
@@ -16,10 +16,11 @@ async fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new async year")
+        .header(ContentType::TEXT_PLAIN)
         .body(String::from("Be happy with async!"))
         .unwrap();
 
-    let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+    let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 
     // Open a remote connection to gmail
     let mailer: AsyncSmtpTransport<Tokio1Executor> =

src/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/0.10.2")]
+#![doc(html_root_url = "https://docs.rs/crate/lettre/0.10.4")]
 #![doc(html_favicon_url = "https://lettre.rs/favicon.ico")]
 #![doc(html_logo_url = "https://avatars0.githubusercontent.com/u/15113230?v=4")]
 #![forbid(unsafe_code)]
@@ -135,6 +135,8 @@
     clippy::manual_assert,
     clippy::unnecessary_join,
     clippy::wildcard_imports,
+    clippy::str_to_string,
+    clippy::empty_structs_with_brackets,
     clippy::zero_sized_map_values
 )]
 #![cfg_attr(docsrs, feature(doc_cfg))]

src/message/dkim.rs

@@ -477,9 +477,9 @@ cJ5Ku0OTwRtSMaseRPX+T4EfG1Caa/eunPPN4rh+CSup2BVVarOT
             .from("Test O'Leary <test+ezrz@example.net>".parse().unwrap())
             .to("Test2 <test2@example.org>".parse().unwrap())
             .date(std::time::UNIX_EPOCH)
-            .header(TestHeader("test  test very very long with spaces and extra spaces   \twill be folded to several lines ".to_string()))
+            .header(TestHeader("test  test very very long with spaces and extra spaces   \twill be folded to several lines ".to_owned()))
             .subject("Test with utf-8 ë")
-            .body("test\r\n\r\ntest   \ttest\r\n\r\n\r\n".to_string()).unwrap()
+            .body("test\r\n\r\ntest   \ttest\r\n\r\n\r\n".to_owned()).unwrap()
     }
 
     #[test]
@@ -521,8 +521,8 @@ cJ5Ku0OTwRtSMaseRPX+T4EfG1Caa/eunPPN4rh+CSup2BVVarOT
         dkim_sign_fixed_time(
             &mut message,
             &DkimConfig::new(
-                "dkimtest".to_string(),
-                "example.org".to_string(),
+                "dkimtest".to_owned(),
+                "example.org".to_owned(),
                 signing_key,
                 vec![
                     HeaderName::new_from_ascii_str("Date"),
@@ -570,8 +570,8 @@ cJ5Ku0OTwRtSMaseRPX+T4EfG1Caa/eunPPN4rh+CSup2BVVarOT
         dkim_sign_fixed_time(
             &mut message,
             &DkimConfig::new(
-                "dkimtest".to_string(),
-                "example.org".to_string(),
+                "dkimtest".to_owned(),
+                "example.org".to_owned(),
                 signing_key,
                 vec![
                     HeaderName::new_from_ascii_str("Date"),

src/message/header/content.rs

@@ -99,7 +99,7 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Transfer-Encoding"),
-            "7bit".to_string(),
+            "7bit".to_owned(),
         ));
 
         assert_eq!(
@@ -109,7 +109,7 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Transfer-Encoding"),
-            "base64".to_string(),
+            "base64".to_owned(),
         ));
 
         assert_eq!(

src/message/header/content_disposition.rs

@@ -16,8 +16,8 @@ impl ContentDisposition {
     pub fn inline() -> Self {
         Self(HeaderValue::dangerous_new_pre_encoded(
             Self::name(),
-            "inline".to_string(),
-            "inline".to_string(),
+            "inline".to_owned(),
+            "inline".to_owned(),
         ))
     }
 
@@ -106,7 +106,7 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Disposition"),
-            "inline".to_string(),
+            "inline".to_owned(),
         ));
 
         assert_eq!(
@@ -116,7 +116,7 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Disposition"),
-            "attachment; filename=\"something.txt\"".to_string(),
+            "attachment; filename=\"something.txt\"".to_owned(),
         ));
 
         assert_eq!(

src/message/header/content_type.rs

@@ -178,14 +178,14 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Type"),
-            "text/plain; charset=utf-8".to_string(),
+            "text/plain; charset=utf-8".to_owned(),
         ));
 
         assert_eq!(headers.get::<ContentType>(), Some(ContentType::TEXT_PLAIN));
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Type"),
-            "text/html; charset=utf-8".to_string(),
+            "text/html; charset=utf-8".to_owned(),
         ));
 
         assert_eq!(headers.get::<ContentType>(), Some(ContentType::TEXT_HTML));

src/message/header/date.rs

@@ -90,7 +90,7 @@ mod test {
 
         assert_eq!(
             headers.to_string(),
-            "Date: Tue, 15 Nov 1994 08:12:31 +0000\r\n".to_string()
+            "Date: Tue, 15 Nov 1994 08:12:31 +0000\r\n".to_owned()
         );
 
         // Tue, 15 Nov 1994 08:12:32 GMT
@@ -110,7 +110,7 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Date"),
-            "Tue, 15 Nov 1994 08:12:31 +0000".to_string(),
+            "Tue, 15 Nov 1994 08:12:31 +0000".to_owned(),
         ));
 
         assert_eq!(
@@ -122,7 +122,7 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Date"),
-            "Tue, 15 Nov 1994 08:12:32 +0000".to_string(),
+            "Tue, 15 Nov 1994 08:12:32 +0000".to_owned(),
         ));
 
         assert_eq!(

src/message/header/mailbox.rs

@@ -252,7 +252,7 @@ mod test {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("From"),
-            "kayo@example.com".to_string(),
+            "kayo@example.com".to_owned(),
         ));
 
         assert_eq!(headers.get::<From>(), Some(From(from)));
@@ -265,7 +265,7 @@ mod test {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("From"),
-            "K. <kayo@example.com>".to_string(),
+            "K. <kayo@example.com>".to_owned(),
         ));
 
         assert_eq!(headers.get::<From>(), Some(From(from)));
@@ -281,7 +281,7 @@ mod test {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("From"),
-            "kayo@example.com, pony@domain.tld".to_string(),
+            "kayo@example.com, pony@domain.tld".to_owned(),
         ));
 
         assert_eq!(headers.get::<From>(), Some(From(from.into())));
@@ -297,7 +297,7 @@ mod test {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("From"),
-            "K. <kayo@example.com>, Pony P. <pony@domain.tld>".to_string(),
+            "K. <kayo@example.com>, Pony P. <pony@domain.tld>".to_owned(),
         ));
 
         assert_eq!(headers.get::<From>(), Some(From(from.into())));
@@ -313,7 +313,7 @@ mod test {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("From"),
-            "Test, test <1@example.com>, Test2, test2 <2@example.com>".to_string(),
+            "Test, test <1@example.com>, Test2, test2 <2@example.com>".to_owned(),
         ));
 
         assert_eq!(headers.get::<From>(), Some(From(from.into())));
@@ -324,7 +324,7 @@ mod test {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("From"),
-            "Test, test <1@example.com>, Test2, test2".to_string(),
+            "Test, test <1@example.com>, Test2, test2".to_owned(),
         ));
 
         assert_eq!(headers.get::<From>(), None);

src/message/header/mod.rs

@@ -474,7 +474,7 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("To"),
-            "John Doe <example@example.com>, Jean Dupont <jean@example.com>".to_string(),
+            "John Doe <example@example.com>, Jean Dupont <jean@example.com>".to_owned(),
         ));
 
         assert_eq!(
@@ -488,7 +488,7 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("To"),
-            "Ascii <example@example.com>, John Doe <johndoe@example.com, John Smith <johnsmith@example.com>, Pinco Pallino <pincopallino@example.com>, Jemand <jemand@example.com>, Jean Dupont <jean@example.com>".to_string(),
+            "Ascii <example@example.com>, John Doe <johndoe@example.com, John Smith <johnsmith@example.com>, Pinco Pallino <pincopallino@example.com>, Jemand <jemand@example.com>, Jean Dupont <jean@example.com>".to_owned(),
         ));
 
         assert_eq!(
@@ -506,7 +506,7 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "Hello! This is lettre, and this IsAVeryLongLineDoYouKnowWhatsGoingToHappenIGuessWeAreGoingToFindOut. Ok I guess that's it!".to_string()
+            "Hello! This is lettre, and this IsAVeryLongLineDoYouKnowWhatsGoingToHappenIGuessWeAreGoingToFindOut. Ok I guess that's it!".to_owned()
         ));
 
         assert_eq!(
@@ -525,7 +525,7 @@ mod tests {
         headers.insert_raw(
             HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "Hello! IGuessTheLastLineWasntLongEnoughSoLetsTryAgainShallWeWhatDoYouThinkItsGoingToHappenIGuessWereAboutToFindOut! I don't know".to_string()
+            "Hello! IGuessTheLastLineWasntLongEnoughSoLetsTryAgainShallWeWhatDoYouThinkItsGoingToHappenIGuessWereAboutToFindOut! I don't know".to_owned()
         ));
 
         assert_eq!(
@@ -543,7 +543,7 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "1abcdefghijklmnopqrstuvwxyz2abcdefghijklmnopqrstuvwxyz3abcdefghijklmnopqrstuvwxyz4abcdefghijklmnopqrstuvwxyz5abcdefghijklmnopqrstuvwxyz6abcdefghijklmnopqrstuvwxyz".to_string()
+            "1abcdefghijklmnopqrstuvwxyz2abcdefghijklmnopqrstuvwxyz3abcdefghijklmnopqrstuvwxyz4abcdefghijklmnopqrstuvwxyz5abcdefghijklmnopqrstuvwxyz6abcdefghijklmnopqrstuvwxyz".to_owned()
         ));
 
         assert_eq!(
@@ -557,7 +557,7 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("To"),
-            "Seán <sean@example.com>".to_string(),
+            "Seán <sean@example.com>".to_owned(),
         ));
 
         assert_eq!(
@@ -571,7 +571,7 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("To"),
-            "🌎 <world@example.com>".to_string(),
+            "🌎 <world@example.com>".to_owned(),
         ));
 
         assert_eq!(
@@ -609,7 +609,7 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("To"),
-            "🌍 <world@example.com>, 🦆 Everywhere <ducks@example.com>, Иванов Иван Иванович <ivanov@example.com>, Jānis Bērziņš <janis@example.com>, Seán Ó Rudaí <sean@example.com>".to_string(),
+            "🌍 <world@example.com>, 🦆 Everywhere <ducks@example.com>, Иванов Иван Иванович <ivanov@example.com>, Jānis Bērziņš <janis@example.com>, Seán Ó Rudaí <sean@example.com>".to_owned(),
         ));
 
         // TODO: fix the fact that the encoder doesn't know that
@@ -633,7 +633,7 @@ mod tests {
         headers.insert_raw(
             HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳".to_string(),)
+            "🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳🥳".to_owned(),)
         );
 
         assert_eq!(
@@ -654,7 +654,7 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "Hello! \r\n This is \" bad \0. 👋".to_string(),
+            "Hello! \r\n This is \" bad \0. 👋".to_owned(),
         ));
 
         assert_eq!(
@@ -669,22 +669,22 @@ mod tests {
         headers.insert_raw(
             HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "Hello! This is lettre, and this IsAVeryLongLineDoYouKnowWhatsGoingToHappenIGuessWeAreGoingToFindOut. Ok I guess that's it!".to_string()
+            "Hello! This is lettre, and this IsAVeryLongLineDoYouKnowWhatsGoingToHappenIGuessWeAreGoingToFindOut. Ok I guess that's it!".to_owned()
             )
         );
         headers.insert_raw(
             HeaderValue::new(
             HeaderName::new_from_ascii_str("To"),
-            "🌍 <world@example.com>, 🦆 Everywhere <ducks@example.com>, Иванов Иван Иванович <ivanov@example.com>, Jānis Bērziņš <janis@example.com>, Seán Ó Rudaí <sean@example.com>".to_string(),
+            "🌍 <world@example.com>, 🦆 Everywhere <ducks@example.com>, Иванов Иван Иванович <ivanov@example.com>, Jānis Bērziņš <janis@example.com>, Seán Ó Rudaí <sean@example.com>".to_owned(),
             )
         );
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("From"),
-            "Someone <somewhere@example.com>".to_string(),
+            "Someone <somewhere@example.com>".to_owned(),
         ));
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Content-Transfer-Encoding"),
-            "quoted-printable".to_string(),
+            "quoted-printable".to_owned(),
         ));
 
         // TODO: fix the fact that the encoder doesn't know that
@@ -712,7 +712,7 @@ mod tests {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "＋仮名 :a;go; ;;;;;s;;;;;;;;;;;;;;;;fffeinmjgggggggggｆっ".to_string(),
+            "＋仮名 :a;go; ;;;;;s;;;;;;;;;;;;;;;;fffeinmjgggggggggｆっ".to_owned(),
         ));
 
         assert_eq!(

src/message/header/special.rs

@@ -91,14 +91,14 @@ mod test {
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("MIME-Version"),
-            "1.0".to_string(),
+            "1.0".to_owned(),
         ));
 
         assert_eq!(headers.get::<MimeVersion>(), Some(MIME_VERSION_1_0));
 
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("MIME-Version"),
-            "0.1".to_string(),
+            "0.1".to_owned(),
         ));
 
         assert_eq!(headers.get::<MimeVersion>(), Some(MimeVersion::new(0, 1)));

src/message/header/textual.rs

@@ -125,7 +125,7 @@ mod test {
         let mut headers = Headers::new();
         headers.insert_raw(HeaderValue::new(
             HeaderName::new_from_ascii_str("Subject"),
-            "Sample subject".to_string(),
+            "Sample subject".to_owned(),
         ));
 
         assert_eq!(

src/message/mailbox/serde.rs

@@ -13,7 +13,7 @@ impl Serialize for Mailbox {
     where
         S: Serializer,
     {
-        serializer.serialize_str(&self.to_string())
+        serializer.collect_str(self)
     }
 }
 
@@ -111,7 +111,7 @@ impl Serialize for Mailboxes {
     where
         S: Serializer,
     {
-        serializer.serialize_str(&self.to_string())
+        serializer.collect_str(self)
     }
 }
 

src/message/mailbox/types.rs

@@ -620,7 +620,7 @@ mod test {
     #[test]
     fn parse_address_from_tuple() {
         assert_eq!(
-            ("K.".to_string(), "kayo@example.com".to_string()).try_into(),
+            ("K.".to_owned(), "kayo@example.com".to_owned()).try_into(),
             Ok(Mailbox::new(
                 Some("K.".into()),
                 "kayo@example.com".parse().unwrap()

src/message/mod.rs

@@ -345,9 +345,9 @@ impl MessageBuilder {
                 let hostname = hostname::get()
                     .map_err(|_| ())
                     .and_then(|s| s.into_string().map_err(|_| ()))
-                    .unwrap_or_else(|_| DEFAULT_MESSAGE_ID_DOMAIN.to_string());
+                    .unwrap_or_else(|_| DEFAULT_MESSAGE_ID_DOMAIN.to_owned());
                 #[cfg(not(feature = "hostname"))]
-                let hostname = DEFAULT_MESSAGE_ID_DOMAIN.to_string();
+                let hostname = DEFAULT_MESSAGE_ID_DOMAIN.to_owned();
 
                 self.header(header::MessageId::from(
                     // https://tools.ietf.org/html/rfc5322#section-3.6.4
@@ -541,7 +541,7 @@ impl Message {
     ///     .reply_to("Bob <bob@example.org>".parse().unwrap())
     ///     .to("Carla <carla@example.net>".parse().unwrap())
     ///     .subject("Hello")
-    ///     .body("Hi there, it's a test email, with utf-8 chars ë!\n\n\n".to_string())
+    ///     .body("Hi there, it's a test email, with utf-8 chars ë!\n\n\n".to_owned())
     ///     .unwrap();
     /// let key = "-----BEGIN RSA PRIVATE KEY-----
     /// MIIEowIBAAKCAQEAt2gawjoybf0mAz0mSX0cq1ah5F9cPazZdCwLnFBhRufxaZB8
@@ -572,8 +572,8 @@ impl Message {
     /// -----END RSA PRIVATE KEY-----";
     /// let signing_key = DkimSigningKey::new(key, DkimSigningAlgorithm::Rsa).unwrap();
     /// message.sign(&DkimConfig::default_config(
-    ///     "dkimtest".to_string(),
-    ///     "example.org".to_string(),
+    ///     "dkimtest".to_owned(),
+    ///     "example.org".to_owned(),
     ///     signing_key,
     /// ));
     /// println!(

src/transport/mod.rs

@@ -65,7 +65,7 @@
 //!     .subject("Happy new year")
 //!     .body(String::from("Be happy!"))?;
 //!
-//! let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
+//! let creds = Credentials::new("smtp_username".to_owned(), "smtp_password".to_owned());
 //!
 //! // Open a remote connection to the SMTP relay server
 //! let mailer = SmtpTransport::relay("smtp.gmail.com")?

src/transport/smtp/authentication.rs

@@ -127,7 +127,7 @@ mod test {
     fn test_plain() {
         let mechanism = Mechanism::Plain;
 
-        let credentials = Credentials::new("username".to_string(), "password".to_string());
+        let credentials = Credentials::new("username".to_owned(), "password".to_owned());
 
         assert_eq!(
             mechanism.response(&credentials, None).unwrap(),
@@ -140,7 +140,7 @@ mod test {
     fn test_login() {
         let mechanism = Mechanism::Login;
 
-        let credentials = Credentials::new("alice".to_string(), "wonderland".to_string());
+        let credentials = Credentials::new("alice".to_owned(), "wonderland".to_owned());
 
         assert_eq!(
             mechanism.response(&credentials, Some("Username")).unwrap(),
@@ -158,8 +158,8 @@ mod test {
         let mechanism = Mechanism::Xoauth2;
 
         let credentials = Credentials::new(
-            "username".to_string(),
-            "vF9dft4qmTc2Nvb3RlckBhdHRhdmlzdGEuY29tCg==".to_string(),
+            "username".to_owned(),
+            "vF9dft4qmTc2Nvb3RlckBhdHRhdmlzdGEuY29tCg==".to_owned(),
         );
 
         assert_eq!(
@@ -172,7 +172,7 @@ mod test {
     #[test]
     fn test_from_user_pass_for_credentials() {
         assert_eq!(
-            Credentials::new("alice".to_string(), "wonderland".to_string()),
+            Credentials::new("alice".to_owned(), "wonderland".to_owned()),
             Credentials::from(("alice", "wonderland"))
         );
     }

src/transport/smtp/client/async_net.rs

@@ -323,7 +323,7 @@ impl AsyncNetworkStream {
         tcp_stream: Box<dyn AsyncTokioStream>,
         tls_parameters: TlsParameters,
     ) -> Result<InnerAsyncNetworkStream, Error> {
-        let domain = tls_parameters.domain().to_string();
+        let domain = tls_parameters.domain().to_owned();
 
         match tls_parameters.connector {
             #[cfg(feature = "native-tls")]

src/transport/smtp/client/mod.rs

@@ -11,7 +11,7 @@
 //!     client::SmtpConnection, commands::*, extension::ClientId, SMTP_PORT,
 //! };
 //!
-//! let hello = ClientId::Domain("my_hostname".to_string());
+//! let hello = ClientId::Domain("my_hostname".to_owned());
 //! let mut client = SmtpConnection::connect(&("localhost", SMTP_PORT), None, &hello, None, None)?;
 //! client.command(Mail::new(Some("user@example.com".parse()?), vec![]))?;
 //! client.command(Rcpt::new("user@example.org".parse()?, vec![]))?;
@@ -38,7 +38,7 @@ pub(super) use self::tls::InnerTlsParameters;
 pub use self::tls::TlsVersion;
 pub use self::{
     connection::SmtpConnection,
-    tls::{Certificate, Tls, TlsParameters, TlsParametersBuilder},
+    tls::{Certificate, CertificateStore, Tls, TlsParameters, TlsParametersBuilder},
 };
 
 #[cfg(any(feature = "tokio1", feature = "async-std1"))]

src/transport/smtp/client/tls.rs

@@ -3,13 +3,16 @@ use std::fmt::{self, Debug};
 use std::{sync::Arc, time::SystemTime};
 
 #[cfg(feature = "boring-tls")]
-use boring::ssl::{SslConnector, SslVersion};
+use boring::{
+    ssl::{SslConnector, SslVersion},
+    x509::store::X509StoreBuilder,
+};
 #[cfg(feature = "native-tls")]
 use native_tls::{Protocol, TlsConnector};
 #[cfg(feature = "rustls-tls")]
 use rustls::{
     client::{ServerCertVerified, ServerCertVerifier, WebPkiVerifier},
-    ClientConfig, Error as TlsError, OwnedTrustAnchor, RootCertStore, ServerName,
+    ClientConfig, Error as TlsError, RootCertStore, ServerName,
 };
 
 #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
@@ -84,16 +87,45 @@ impl Debug for Tls {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match &self {
             Self::None => f.pad("None"),
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
             Self::Opportunistic(_) => f.pad("Opportunistic"),
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
             Self::Required(_) => f.pad("Required"),
-            #[cfg(any(feature = "native-tls", feature = "rustls-tls", feature = "boring-tls"))]
+            #[cfg(any(feature = "native-tls", feature = "rustls", feature = "boring-tls"))]
             Self::Wrapper(_) => f.pad("Wrapper"),
         }
     }
 }
 
+/// Source for the base set of root certificates to trust.
+#[allow(missing_copy_implementations)]
+#[derive(Clone, Debug)]
+pub enum CertificateStore {
+    /// Use the default for the TLS backend.
+    ///
+    /// For native-tls, this will use the system certificate store on Windows, the keychain on
+    /// macOS, and OpenSSL directories on Linux (usually `/etc/ssl`).
+    ///
+    /// For rustls, this will also use the the system store if the `rustls-native-certs` feature is
+    /// enabled, or will fall back to `webpki-roots`.
+    ///
+    /// The boring-tls backend uses the same logic as OpenSSL on all platforms.
+    Default,
+    /// Use a hardcoded set of Mozilla roots via the `webpki-roots` crate.
+    ///
+    /// This option is only available in the rustls backend.
+    #[cfg(feature = "webpki-roots")]
+    WebpkiRoots,
+    /// Don't use any system certificates.
+    None,
+}
+
+impl Default for CertificateStore {
+    fn default() -> Self {
+        CertificateStore::Default
+    }
+}
+
 /// Parameters to use for secure clients
 #[derive(Clone)]
 pub struct TlsParameters {
@@ -108,6 +140,7 @@ pub struct TlsParameters {
 #[derive(Debug, Clone)]
 pub struct TlsParametersBuilder {
     domain: String,
+    cert_store: CertificateStore,
     root_certs: Vec<Certificate>,
     accept_invalid_hostnames: bool,
     accept_invalid_certs: bool,
@@ -120,6 +153,7 @@ impl TlsParametersBuilder {
     pub fn new(domain: String) -> Self {
         Self {
             domain,
+            cert_store: CertificateStore::Default,
             root_certs: Vec::new(),
             accept_invalid_hostnames: false,
             accept_invalid_certs: false,
@@ -128,6 +162,12 @@ impl TlsParametersBuilder {
         }
     }
 
+    /// Set the source for the base set of root certificates to trust.
+    pub fn certificate_store(mut self, cert_store: CertificateStore) -> Self {
+        self.cert_store = cert_store;
+        self
+    }
+
     /// Add a custom root certificate
     ///
     /// Can be used to safely connect to a server using a self signed certificate, for example.
@@ -208,6 +248,18 @@ impl TlsParametersBuilder {
     pub fn build_native(self) -> Result<TlsParameters, Error> {
         let mut tls_builder = TlsConnector::builder();
 
+        match self.cert_store {
+            CertificateStore::Default => {}
+            CertificateStore::None => {
+                tls_builder.disable_built_in_roots(true);
+            }
+            #[allow(unreachable_patterns)]
+            other => {
+                return Err(error::tls(format!(
+                    "{other:?} is not supported in native tls"
+                )))
+            }
+        }
         for cert in self.root_certs {
             tls_builder.add_root_certificate(cert.native_tls);
         }
@@ -246,6 +298,21 @@ impl TlsParametersBuilder {
         if self.accept_invalid_certs {
             tls_builder.set_verify(SslVerifyMode::NONE);
         } else {
+            match self.cert_store {
+                CertificateStore::Default => {}
+                CertificateStore::None => {
+                    // Replace the default store with an empty store.
+                    tls_builder
+                        .set_cert_store(X509StoreBuilder::new().map_err(error::tls)?.build());
+                }
+                #[allow(unreachable_patterns)]
+                other => {
+                    return Err(error::tls(format!(
+                        "{other:?} is not supported in boring tls"
+                    )))
+                }
+            }
+
             let cert_store = tls_builder.cert_store_mut();
 
             for cert in self.root_certs {
@@ -299,20 +366,58 @@ impl TlsParametersBuilder {
             tls.with_custom_certificate_verifier(Arc::new(InvalidCertsVerifier {}))
         } else {
             let mut root_cert_store = RootCertStore::empty();
+
+            #[cfg(feature = "rustls-native-certs")]
+            fn load_native_roots(store: &mut RootCertStore) -> Result<(), Error> {
+                let native_certs = rustls_native_certs::load_native_certs().map_err(error::tls)?;
+                let mut valid_count = 0;
+                let mut invalid_count = 0;
+                for cert in native_certs {
+                    match store.add(&rustls::Certificate(cert.0)) {
+                        Ok(_) => valid_count += 1,
+                        Err(err) => {
+                            #[cfg(feature = "tracing")]
+                            tracing::debug!("certificate parsing failed: {:?}", err);
+                            invalid_count += 1;
+                        }
+                    }
+                }
+                #[cfg(feature = "tracing")]
+                tracing::debug!(
+                    "loaded platform certs with {valid_count} valid and {invalid_count} invalid certs"
+                );
+                Ok(())
+            }
+
+            #[cfg(feature = "webpki-roots")]
+            fn load_webpki_roots(store: &mut RootCertStore) {
+                store.add_server_trust_anchors(webpki_roots::TLS_SERVER_ROOTS.0.iter().map(|ta| {
+                    rustls::OwnedTrustAnchor::from_subject_spki_name_constraints(
+                        ta.subject,
+                        ta.spki,
+                        ta.name_constraints,
+                    )
+                }));
+            }
+
+            match self.cert_store {
+                CertificateStore::Default => {
+                    #[cfg(feature = "rustls-native-certs")]
+                    load_native_roots(&mut root_cert_store)?;
+                    #[cfg(all(not(feature = "rustls-native-certs"), feature = "webpki-roots"))]
+                    load_webpki_roots(&mut root_cert_store);
+                }
+                #[cfg(feature = "webpki-roots")]
+                CertificateStore::WebpkiRoots => {
+                    load_webpki_roots(&mut root_cert_store);
+                }
+                CertificateStore::None => {}
+            }
             for cert in self.root_certs {
                 for rustls_cert in cert.rustls {
                     root_cert_store.add(&rustls_cert).map_err(error::tls)?;
                 }
             }
-            root_cert_store.add_server_trust_anchors(webpki_roots::TLS_SERVER_ROOTS.0.iter().map(
-                |ta| {
-                    OwnedTrustAnchor::from_subject_spki_name_constraints(
-                        ta.subject,
-                        ta.spki,
-                        ta.name_constraints,
-                    )
-                },
-            ));
 
             tls.with_custom_certificate_verifier(Arc::new(WebPkiVerifier::new(
                 root_cert_store,

src/transport/smtp/commands.rs

@@ -296,15 +296,15 @@ mod test {
 
     #[test]
     fn test_display() {
-        let id = ClientId::Domain("localhost".to_string());
+        let id = ClientId::Domain("localhost".to_owned());
         let email = Address::from_str("test@example.com").unwrap();
         let mail_parameter = MailParameter::Other {
-            keyword: "TEST".to_string(),
-            value: Some("value".to_string()),
+            keyword: "TEST".to_owned(),
+            value: Some("value".to_owned()),
         };
         let rcpt_parameter = RcptParameter::Other {
-            keyword: "TEST".to_string(),
-            value: Some("value".to_string()),
+            keyword: "TEST".to_owned(),
+            value: Some("value".to_owned()),
         };
         assert_eq!(format!("{}", Ehlo::new(id)), "EHLO localhost\r\n");
         assert_eq!(
@@ -346,19 +346,13 @@ mod test {
         assert_eq!(format!("{Noop}"), "NOOP\r\n");
         assert_eq!(format!("{}", Help::new(None)), "HELP\r\n");
         assert_eq!(
-            format!("{}", Help::new(Some("test".to_string()))),
+            format!("{}", Help::new(Some("test".to_owned()))),
             "HELP test\r\n"
         );
-        assert_eq!(
-            format!("{}", Vrfy::new("test".to_string())),
-            "VRFY test\r\n"
-        );
-        assert_eq!(
-            format!("{}", Expn::new("test".to_string())),
-            "EXPN test\r\n"
-        );
+        assert_eq!(format!("{}", Vrfy::new("test".to_owned())), "VRFY test\r\n");
+        assert_eq!(format!("{}", Expn::new("test".to_owned())), "EXPN test\r\n");
         assert_eq!(format!("{Rset}"), "RSET\r\n");
-        let credentials = Credentials::new("user".to_string(), "password".to_string());
+        let credentials = Credentials::new("user".to_owned(), "password".to_owned());
         assert_eq!(
             format!(
                 "{}",

src/transport/smtp/extension.rs

@@ -119,7 +119,7 @@ pub struct ServerInfo {
 impl Display for ServerInfo {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         let features = if self.features.is_empty() {
-            "no supported features".to_string()
+            "no supported features".to_owned()
         } else {
             format!("{:?}", self.features)
         };
@@ -174,7 +174,7 @@ impl ServerInfo {
         }
 
         Ok(ServerInfo {
-            name: name.to_string(),
+            name: name.to_owned(),
             features,
         })
     }
@@ -304,21 +304,21 @@ mod test {
     #[test]
     fn test_clientid_fmt() {
         assert_eq!(
-            format!("{}", ClientId::Domain("test".to_string())),
-            "test".to_string()
+            format!("{}", ClientId::Domain("test".to_owned())),
+            "test".to_owned()
         );
-        assert_eq!(format!("{LOCALHOST_CLIENT}"), "[127.0.0.1]".to_string());
+        assert_eq!(format!("{LOCALHOST_CLIENT}"), "[127.0.0.1]".to_owned());
     }
 
     #[test]
     fn test_extension_fmt() {
         assert_eq!(
             format!("{}", Extension::EightBitMime),
-            "8BITMIME".to_string()
+            "8BITMIME".to_owned()
         );
         assert_eq!(
             format!("{}", Extension::Authentication(Mechanism::Plain)),
-            "AUTH PLAIN".to_string()
+            "AUTH PLAIN".to_owned()
         );
     }
 
@@ -331,11 +331,11 @@ mod test {
             format!(
                 "{}",
                 ServerInfo {
-                    name: "name".to_string(),
+                    name: "name".to_owned(),
                     features: eightbitmime,
                 }
             ),
-            "name with {EightBitMime}".to_string()
+            "name with {EightBitMime}".to_owned()
         );
 
         let empty = HashSet::new();
@@ -344,11 +344,11 @@ mod test {
             format!(
                 "{}",
                 ServerInfo {
-                    name: "name".to_string(),
+                    name: "name".to_owned(),
                     features: empty,
                 }
             ),
-            "name with no supported features".to_string()
+            "name with no supported features".to_owned()
         );
 
         let mut plain = HashSet::new();
@@ -358,11 +358,11 @@ mod test {
             format!(
                 "{}",
                 ServerInfo {
-                    name: "name".to_string(),
+                    name: "name".to_owned(),
                     features: plain,
                 }
             ),
-            "name with {Authentication(Plain)}".to_string()
+            "name with {Authentication(Plain)}".to_owned()
         );
     }
 
@@ -374,18 +374,14 @@ mod test {
                 Category::Unspecified4,
                 Detail::One,
             ),
-            vec![
-                "me".to_string(),
-                "8BITMIME".to_string(),
-                "SIZE 42".to_string(),
-            ],
+            vec!["me".to_owned(), "8BITMIME".to_owned(), "SIZE 42".to_owned()],
         );
 
         let mut features = HashSet::new();
         assert!(features.insert(Extension::EightBitMime));
 
         let server_info = ServerInfo {
-            name: "me".to_string(),
+            name: "me".to_owned(),
             features,
         };
 
@@ -401,10 +397,10 @@ mod test {
                 Detail::One,
             ),
             vec![
-                "me".to_string(),
-                "AUTH PLAIN CRAM-MD5 XOAUTH2 OTHER".to_string(),
-                "8BITMIME".to_string(),
-                "SIZE 42".to_string(),
+                "me".to_owned(),
+                "AUTH PLAIN CRAM-MD5 XOAUTH2 OTHER".to_owned(),
+                "8BITMIME".to_owned(),
+                "SIZE 42".to_owned(),
             ],
         );
 
@@ -414,7 +410,7 @@ mod test {
         assert!(features2.insert(Extension::Authentication(Mechanism::Xoauth2),));
 
         let server_info2 = ServerInfo {
-            name: "me".to_string(),
+            name: "me".to_owned(),
             features: features2,
         };
 

src/transport/smtp/mod.rs

@@ -77,8 +77,8 @@
 //! let sender = SmtpTransport::starttls_relay("smtp.example.com")?
 //!     // Add credentials for authentication
 //!     .credentials(Credentials::new(
-//!         "username".to_string(),
-//!         "password".to_string(),
+//!         "username".to_owned(),
+//!         "password".to_owned(),
 //!     ))
 //!     // Configure expected authentication mechanism
 //!     .authentication(vec![Mechanism::Plain])
@@ -111,7 +111,7 @@
 //!     .body(String::from("Be happy!"))?;
 //!
 //! // Custom TLS configuration
-//! let tls = TlsParameters::builder("smtp.example.com".to_string())
+//! let tls = TlsParameters::builder("smtp.example.com".to_owned())
 //!     .dangerous_accept_invalid_certs(true)
 //!     .build()?;
 //!
@@ -200,7 +200,7 @@ struct SmtpInfo {
 impl Default for SmtpInfo {
     fn default() -> Self {
         Self {
-            server: "localhost".to_string(),
+            server: "localhost".to_owned(),
             port: SMTP_PORT,
             hello_name: ClientId::default(),
             credentials: None,

src/transport/smtp/pool/async_impl.rs

@@ -203,7 +203,7 @@ impl<E: Executor> Debug for Pool<E> {
                 &match self.connections.try_lock() {
                     Some(connections) => format!("{} connections", connections.len()),
 
-                    None => "LOCKED".to_string(),
+                    None => "LOCKED".to_owned(),
                 },
             )
             .field("client", &self.client)

src/transport/smtp/pool/sync_impl.rs

@@ -186,8 +186,8 @@ impl Debug for Pool {
                 &match self.connections.try_lock() {
                     Ok(connections) => format!("{} connections", connections.len()),
 
-                    Err(TryLockError::WouldBlock) => "LOCKED".to_string(),
-                    Err(TryLockError::Poisoned(_)) => "POISONED".to_string(),
+                    Err(TryLockError::WouldBlock) => "LOCKED".to_owned(),
+                    Err(TryLockError::Poisoned(_)) => "POISONED".to_owned(),
                 },
             )
             .field("client", &self.client)

src/transport/smtp/response.rs

@@ -151,7 +151,7 @@ impl FromStr for Response {
     fn from_str(s: &str) -> result::Result<Response, Error> {
         parse_response(s)
             .map(|(_, r)| r)
-            .map_err(|e| error::response(e.to_string()))
+            .map_err(|e| error::response(e.to_owned()))
     }
 }
 
@@ -329,10 +329,10 @@ mod test {
                     detail: Detail::Zero,
                 },
                 message: vec![
-                    "me".to_string(),
-                    "8BITMIME".to_string(),
-                    "SIZE 42".to_string(),
-                    "AUTH PLAIN CRAM-MD5".to_string(),
+                    "me".to_owned(),
+                    "8BITMIME".to_owned(),
+                    "SIZE 42".to_owned(),
+                    "AUTH PLAIN CRAM-MD5".to_owned(),
                 ],
             }
         );
@@ -352,11 +352,7 @@ mod test {
                 category: Category::MailSystem,
                 detail: Detail::Zero,
             },
-            vec![
-                "me".to_string(),
-                "8BITMIME".to_string(),
-                "SIZE 42".to_string(),
-            ],
+            vec!["me".to_owned(), "8BITMIME".to_owned(), "SIZE 42".to_owned(),],
         )
         .is_positive());
         assert!(!Response::new(
@@ -365,11 +361,7 @@ mod test {
                 category: Category::MailSystem,
                 detail: Detail::Zero,
             },
-            vec![
-                "me".to_string(),
-                "8BITMIME".to_string(),
-                "SIZE 42".to_string(),
-            ],
+            vec!["me".to_owned(), "8BITMIME".to_owned(), "SIZE 42".to_owned(),],
         )
         .is_positive());
     }
@@ -382,11 +374,7 @@ mod test {
                 category: Category::MailSystem,
                 detail: Detail::One,
             },
-            vec![
-                "me".to_string(),
-                "8BITMIME".to_string(),
-                "SIZE 42".to_string(),
-            ],
+            vec!["me".to_owned(), "8BITMIME".to_owned(), "SIZE 42".to_owned(),],
         )
         .has_code(451));
         assert!(!Response::new(
@@ -395,11 +383,7 @@ mod test {
                 category: Category::MailSystem,
                 detail: Detail::One,
             },
-            vec![
-                "me".to_string(),
-                "8BITMIME".to_string(),
-                "SIZE 42".to_string(),
-            ],
+            vec!["me".to_owned(), "8BITMIME".to_owned(), "SIZE 42".to_owned(),],
         )
         .has_code(251));
     }
@@ -413,11 +397,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec![
-                    "me".to_string(),
-                    "8BITMIME".to_string(),
-                    "SIZE 42".to_string(),
-                ],
+                vec!["me".to_owned(), "8BITMIME".to_owned(), "SIZE 42".to_owned(),],
             )
             .first_word(),
             Some("me")
@@ -430,9 +410,9 @@ mod test {
                     detail: Detail::One,
                 },
                 vec![
-                    "me mo".to_string(),
-                    "8BITMIME".to_string(),
-                    "SIZE 42".to_string(),
+                    "me mo".to_owned(),
+                    "8BITMIME".to_owned(),
+                    "SIZE 42".to_owned(),
                 ],
             )
             .first_word(),
@@ -457,7 +437,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec![" ".to_string()],
+                vec![" ".to_owned()],
             )
             .first_word(),
             None
@@ -469,7 +449,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec!["  ".to_string()],
+                vec!["  ".to_owned()],
             )
             .first_word(),
             None
@@ -481,7 +461,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec!["".to_string()],
+                vec!["".to_owned()],
             )
             .first_word(),
             None
@@ -507,11 +487,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec![
-                    "me".to_string(),
-                    "8BITMIME".to_string(),
-                    "SIZE 42".to_string(),
-                ],
+                vec!["me".to_owned(), "8BITMIME".to_owned(), "SIZE 42".to_owned(),],
             )
             .first_line(),
             Some("me")
@@ -524,9 +500,9 @@ mod test {
                     detail: Detail::One,
                 },
                 vec![
-                    "me mo".to_string(),
-                    "8BITMIME".to_string(),
-                    "SIZE 42".to_string(),
+                    "me mo".to_owned(),
+                    "8BITMIME".to_owned(),
+                    "SIZE 42".to_owned(),
                 ],
             )
             .first_line(),
@@ -551,7 +527,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec![" ".to_string()],
+                vec![" ".to_owned()],
             )
             .first_line(),
             Some(" ")
@@ -563,7 +539,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec!["  ".to_string()],
+                vec!["  ".to_owned()],
             )
             .first_line(),
             Some("  ")
@@ -575,7 +551,7 @@ mod test {
                     category: Category::MailSystem,
                     detail: Detail::One,
                 },
-                vec!["".to_string()],
+                vec!["".to_owned()],
             )
             .first_line(),
             Some("")

src/transport/smtp/util.rs

@@ -41,7 +41,7 @@ mod tests {
         ]
         .iter()
         {
-            assert_eq!(format!("{}", XText(input)), (*expect).to_string());
+            assert_eq!(format!("{}", XText(input)), (*expect).to_owned());
         }
     }
 }