feat: Add experimental option to disable mailboxes (#108)

Signed-off-by: Jagoda Ślązak <jslazak@jslazak.com>

filtermail/src/config.rs

@@ -72,17 +72,29 @@ impl Config {
         }
     }
 
-    /// Check if not encrypted mail is allowed for the given address.
-    pub fn is_cleartext_ok(&self, addr: &str) -> bool {
+    /// Check if a specific flag file exists for the given address.
+    ///
+    /// Returns `default` if the address is invalid.
+    fn check_flag(&self, addr: &str, flag: &str, default: bool) -> bool {
         if addr.is_empty() || !addr.contains('@') || addr.contains('/') {
-            return false;
+            return default;
         }
 
-        let mut enforce_e2ee = self.mailboxes_dir();
-        enforce_e2ee.push(addr);
-        enforce_e2ee.push("enforceE2EEincoming");
+        let mut path = self.mailboxes_dir();
+        path.push(addr);
+        path.push(flag);
 
-        !enforce_e2ee.exists()
+        path.exists()
+    }
+
+    /// Check if not encrypted mail is allowed for the given address.
+    pub fn is_cleartext_ok(&self, addr: &str) -> bool {
+        !self.check_flag(addr, "enforceE2EEincoming", true)
+    }
+
+    /// Check if the given address is disabled.
+    pub fn is_disabled(&self, addr: &str) -> bool {
+        self.check_flag(addr, "DISABLED", false)
     }
 
     // Following are needed since serde does not support default literals.

filtermail/src/inbound.rs

@@ -98,6 +98,13 @@ impl SmtpHandler for IncomingBeforeQueueHandler {
             envelope.mail_from = String::new();
         }
 
+        envelope.rcpt_to = envelope
+            .rcpt_to
+            .iter()
+            .filter(|s| !self.config.is_disabled(s))
+            .cloned()
+            .collect();
+
         let mail_encrypted = check_encrypted(&message, false);
         log::debug!("mail_encrypted: {mail_encrypted}");
         log::debug!("is_securejoin: {}", is_securejoin(&message));

filtermail/src/outbound.rs

@@ -78,6 +78,13 @@ impl SmtpHandler for OutgoingBeforeQueueHandler {
         let from_addr = extract_address(&from_header)
             .ok_or(format!("500 Invalid FROM header: {from_header}"))?;
 
+        envelope.rcpt_to = envelope
+            .rcpt_to
+            .iter()
+            .filter(|s| !self.config.is_disabled(s))
+            .cloned()
+            .collect();
+
         // MAIL FROM is our source of truth for outbound messages,
         // as this address is checked by postfix against the username before sending it
         // to filtermail.
@@ -139,4 +146,22 @@ impl SmtpHandler for OutgoingBeforeQueueHandler {
 
         Ok(())
     }
+
+    async fn handle_data(&self, envelope: &mut Envelope) -> Result<String, String> {
+        log::debug!("handle_DATA before-queue");
+        self.check_data(envelope).await?;
+        if self.config.is_disabled(&envelope.mail_from) {
+            log::warn!("Dropping mail; Sender {} is disabled.", envelope.mail_from);
+            return Ok("250 OK".to_string());
+        }
+        if envelope.rcpt_to.is_empty() {
+            log::warn!("Dropping mail; All recipients disabled.");
+            return Ok("250 OK".to_string());
+        }
+        self.reinject_mail(envelope).await.map_err(|e| {
+            log::warn!("Failed to reinject mail: {e}");
+            e
+        })?;
+        Ok("250 OK".to_string())
+    }
 }

filtermail/src/smtp_server.rs

@@ -33,6 +33,10 @@ pub trait SmtpHandler: Send + Sync {
     async fn handle_data(&self, envelope: &mut Envelope) -> Result<String, String> {
         log::debug!("handle_DATA before-queue");
         self.check_data(envelope).await?;
+        if envelope.rcpt_to.is_empty() {
+            log::warn!("Dropping mail; All recipients disabled.");
+            return Ok("250 OK".to_string());
+        }
         self.reinject_mail(envelope).await.map_err(|e| {
             log::warn!("Failed to reinject mail: {e}");
             e