Add support for sendmail as a mail transport

.env.template

@@ -373,7 +373,7 @@
 # ROCKET_WORKERS=10
 # ROCKET_TLS={certs="/path/to/certs.pem",key="/path/to/key.pem"}
 
-## Mail specific settings, set SMTP_HOST and SMTP_FROM to enable the mail service.
+## Mail specific settings, set SMTP_FROM and either SMTP_HOST or USE_SENDMAIL to enable the mail service.
 ## To make sure the email links are pointing to the correct host, set the DOMAIN variable.
 ## Note: if SMTP_USERNAME is specified, SMTP_PASSWORD is mandatory
 # SMTP_HOST=smtp.domain.tld
@@ -385,6 +385,11 @@
 # SMTP_PASSWORD=password
 # SMTP_TIMEOUT=15
 
+# Whether to send mail via the `sendmail` command
+# USE_SENDMAIL=false
+# Which sendmail command to use. The one found in the $PATH is used if not specified.
+# SENDMAIL_COMMAND="/path/to/sendmail"
+
 ## Defaults for SSL is "Plain" and "Login" and nothing for Non-SSL connections.
 ## Possible values: ["Plain", "Login", "Xoauth2"].
 ## Multiple options need to be separated by a comma ','.

Cargo.toml

@@ -114,7 +114,7 @@ webauthn-rs = "0.3.2"
 url = "2.3.1"
 
 # Email librariese-Base, Update crates and small change.
-lettre = { version = "0.10.1", features = ["smtp-transport", "builder", "serde", "tokio1-native-tls", "hostname", "tracing", "tokio1"], default-features = false }
+lettre = { version = "0.10.1", features = ["smtp-transport", "sendmail-transport", "builder", "serde", "tokio1-native-tls", "hostname", "tracing", "tokio1"], default-features = false }
 percent-encoding = "2.2.0" # URL encoding library used for URL's in the emails
 email_address = "0.2.4"
 

src/config.rs

@@ -614,6 +614,10 @@ make_config! {
     smtp: _enable_smtp {
         /// Enabled
         _enable_smtp:                  bool,   true,   def,     true;
+        /// Use Sendmail |> Whether to send mail via the `sendmail` command
+        use_sendmail:                  bool,   true,   def,     false;
+        /// Sendmail Command |> Which sendmail command to use. The one found in the $PATH is used if not specified.
+        sendmail_command:              String, true,   option;
         /// Host
         smtp_host:                     String, true,   option;
         /// DEPRECATED smtp_ssl |> DEPRECATED - Please use SMTP_SECURITY
@@ -653,7 +657,7 @@ make_config! {
     /// Email 2FA Settings
     email_2fa: _enable_email_2fa {
         /// Enabled |> Disabling will prevent users from setting up new email 2FA and using existing email 2FA configured
-        _enable_email_2fa:      bool,   true,   auto,    |c| c._enable_smtp && c.smtp_host.is_some();
+        _enable_email_2fa:      bool,   true,   auto,    |c| c._enable_smtp && (c.smtp_host.is_some() || c.use_sendmail);
         /// Email token size |> Number of digits in an email 2FA token (min: 6, max: 255). Note that the Bitwarden clients are hardcoded to mention 6 digit codes regardless of this setting.
         email_token_size:       u8,     true,   def,      6;
         /// Token expiration time |> Maximum time in seconds a token is valid. The time the user has to open email client and copy token.
@@ -744,27 +748,59 @@ fn validate_config(cfg: &ConfigItems) -> Result<(), Error> {
             ),
         }
 
-        if cfg.smtp_host.is_some() == cfg.smtp_from.is_empty() {
+        if cfg.use_sendmail {
-            err!("Both `SMTP_HOST` and `SMTP_FROM` need to be set for email support")
+            if let Some(ref command) = cfg.sendmail_command {
+                let path = std::path::Path::new(&command);
+
+                if !path.is_absolute() {
+                    err!(format!("path to sendmail command `{path:?}` is not absolute"));
+                }
+
+                match path.metadata() {
+                    Err(err) if err.kind() == std::io::ErrorKind::NotFound => {
+                        err!(format!("sendmail command not found at `{path:?}`"))
+                    }
+                    Err(err) => {
+                        err!(format!("failed to access sendmail command at `{path:?}`: {err}"))
+                    }
+                    Ok(metadata) => {
+                        if metadata.is_dir() {
+                            err!(format!("sendmail command at `{path:?}` isn't a directory"));
+                        }
+
+                        #[cfg(unix)]
+                        {
+                            use std::os::unix::fs::PermissionsExt;
+                            if !metadata.permissions().mode() & 0o111 != 0 {
+                                err!(format!("sendmail command at `{path:?}` isn't executable"));
+                            }
+                        }
+                    }
+                }
+            }
+        } else {
+            if cfg.smtp_host.is_some() == cfg.smtp_from.is_empty() {
+                err!("Both `SMTP_HOST` and `SMTP_FROM` need to be set for email support without `USE_SENDMAIL`")
+            }
+
+            if cfg.smtp_username.is_some() != cfg.smtp_password.is_some() {
+                err!("Both `SMTP_USERNAME` and `SMTP_PASSWORD` need to be set to enable email authentication without `USE_SENDMAIL`")
+            }
         }
 
-        if cfg.smtp_host.is_some() && !cfg.smtp_from.contains('@') {
+        if (cfg.smtp_host.is_some() || cfg.use_sendmail) && !cfg.smtp_from.contains('@') {
             err!("SMTP_FROM does not contain a mandatory @ sign")
         }
 
-        if cfg.smtp_username.is_some() != cfg.smtp_password.is_some() {
-            err!("Both `SMTP_USERNAME` and `SMTP_PASSWORD` need to be set to enable email authentication")
-        }
-
-        if cfg._enable_email_2fa && (!cfg._enable_smtp || cfg.smtp_host.is_none()) {
-            err!("To enable email 2FA, SMTP must be configured")
-        }
-
         if cfg._enable_email_2fa && cfg.email_token_size < 6 {
             err!("`EMAIL_TOKEN_SIZE` has a minimum size of 6")
         }
     }
 
+    if cfg._enable_email_2fa && !(cfg.smtp_host.is_some() || cfg.use_sendmail) {
+        err!("To enable email 2FA, a mail transport must be configured")
+    }
+
     // Check if the icon blacklist regex is valid
     if let Some(ref r) = cfg.icon_blacklist_regex {
         let validate_regex = regex::Regex::new(r);
@@ -1045,7 +1081,7 @@ impl Config {
     }
     pub fn mail_enabled(&self) -> bool {
         let inner = &self.inner.read().unwrap().config;
-        inner._enable_smtp && inner.smtp_host.is_some()
+        inner._enable_smtp && (inner.smtp_host.is_some() || inner.use_sendmail)
     }
 
     pub fn get_duo_akey(&self) -> String {

src/mail.rs

@@ -8,7 +8,7 @@ use lettre::{
     transport::smtp::authentication::{Credentials, Mechanism as SmtpAuthMechanism},
     transport::smtp::client::{Tls, TlsParameters},
     transport::smtp::extension::ClientId,
-    Address, AsyncSmtpTransport, AsyncTransport, Tokio1Executor,
+    Address, AsyncSendmailTransport, AsyncSmtpTransport, AsyncTransport, Tokio1Executor,
 };
 
 use crate::{
@@ -21,7 +21,15 @@ use crate::{
     CONFIG,
 };
 
-fn mailer() -> AsyncSmtpTransport<Tokio1Executor> {
+fn sendmail_transport() -> AsyncSendmailTransport<Tokio1Executor> {
+    if let Some(command) = CONFIG.sendmail_command() {
+        AsyncSendmailTransport::new_with_command(command)
+    } else {
+        AsyncSendmailTransport::new()
+    }
+}
+
+fn smtp_transport() -> AsyncSmtpTransport<Tokio1Executor> {
     use std::time::Duration;
     let host = CONFIG.smtp_host().unwrap();
 
@@ -509,6 +517,58 @@ pub async fn send_admin_reset_password(address: &str, user_name: &str, org_name:
     send_email(address, &subject, body_html, body_text).await
 }
 
+async fn send_with_selected_transport(email: Message) -> EmptyResult {
+    if CONFIG.use_sendmail() {
+        match sendmail_transport().send(email).await {
+            Ok(_) => Ok(()),
+            // Match some common errors and make them more user friendly
+            Err(e) => {
+                if e.is_client() {
+                    debug!("Sendmail client error: {:#?}", e);
+                    err!(format!("Sendmail client error: {e}"));
+                } else if e.is_response() {
+                    debug!("Sendmail response error: {:#?}", e);
+                    err!(format!("Sendmail response error: {e}"));
+                } else {
+                    debug!("Sendmail error: {:#?}", e);
+                    err!(format!("Sendmail error: {e}"));
+                }
+            }
+        }
+    } else {
+        match smtp_transport().send(email).await {
+            Ok(_) => Ok(()),
+            // Match some common errors and make them more user friendly
+            Err(e) => {
+                if e.is_client() {
+                    debug!("SMTP client error: {:#?}", e);
+                    err!(format!("SMTP client error: {e}"));
+                } else if e.is_transient() {
+                    debug!("SMTP 4xx error: {:#?}", e);
+                    err!(format!("SMTP 4xx error: {e}"));
+                } else if e.is_permanent() {
+                    debug!("SMTP 5xx error: {:#?}", e);
+                    let mut msg = e.to_string();
+                    // Add a special check for 535 to add a more descriptive message
+                    if msg.contains("(535)") {
+                        msg = format!("{msg} - Authentication credentials invalid");
+                    }
+                    err!(format!("SMTP 5xx error: {msg}"));
+                } else if e.is_timeout() {
+                    debug!("SMTP timeout error: {:#?}", e);
+                    err!(format!("SMTP timeout error: {e}"));
+                } else if e.is_tls() {
+                    debug!("SMTP encryption error: {:#?}", e);
+                    err!(format!("SMTP encryption error: {e}"));
+                } else {
+                    debug!("SMTP error: {:#?}", e);
+                    err!(format!("SMTP error: {e}"));
+                }
+            }
+        }
+    }
+}
+
 async fn send_email(address: &str, subject: &str, body_html: String, body_text: String) -> EmptyResult {
     let smtp_from = &CONFIG.smtp_from();
 
@@ -538,34 +598,5 @@ async fn send_email(address: &str, subject: &str, body_html: String, body_text:
         .subject(subject)
         .multipart(body)?;
 
-    match mailer().send(email).await {
+    send_with_selected_transport(email).await
-        Ok(_) => Ok(()),
-        // Match some common errors and make them more user friendly
-        Err(e) => {
-            if e.is_client() {
-                debug!("SMTP Client error: {:#?}", e);
-                err!(format!("SMTP Client error: {e}"));
-            } else if e.is_transient() {
-                debug!("SMTP 4xx error: {:#?}", e);
-                err!(format!("SMTP 4xx error: {e}"));
-            } else if e.is_permanent() {
-                debug!("SMTP 5xx error: {:#?}", e);
-                let mut msg = e.to_string();
-                // Add a special check for 535 to add a more descriptive message
-                if msg.contains("(535)") {
-                    msg = format!("{msg} - Authentication credentials invalid");
-                }
-                err!(format!("SMTP 5xx error: {msg}"));
-            } else if e.is_timeout() {
-                debug!("SMTP timeout error: {:#?}", e);
-                err!(format!("SMTP timeout error: {e}"));
-            } else if e.is_tls() {
-                debug!("SMTP Encryption error: {:#?}", e);
-                err!(format!("SMTP Encryption error: {e}"));
-            } else {
-                debug!("SMTP {:#?}", e);
-                err!(format!("SMTP {e}"));
-            }
-        }
-    }
 }