feat(mailer-smtp): add SCRAM-SHA-256 auth, Ed25519 DKIM, opportunistic TLS, SNI cert selection, pipelining and delivery/bridge improvements

rust/crates/mailer-smtp/src/client/protocol.rs

@@ -318,6 +318,54 @@ pub async fn send_rcpt_to(
     Ok(resp)
 }
 
+/// Send MAIL FROM + RCPT TO commands in a single pipelined batch.
+///
+/// Writes all envelope commands at once, then reads responses in order.
+/// Returns `(mail_from_ok, accepted_recipients, rejected_recipients)`.
+pub async fn send_pipelined_envelope(
+    stream: &mut ClientSmtpStream,
+    sender: &str,
+    recipients: &[String],
+    timeout_secs: u64,
+) -> Result<(bool, Vec<String>, Vec<String>), SmtpClientError> {
+    // Build the full pipelined command batch
+    let mut batch = format!("MAIL FROM:<{sender}>\r\n");
+    for rcpt in recipients {
+        batch.push_str(&format!("RCPT TO:<{rcpt}>\r\n"));
+    }
+
+    // Send all commands at once
+    debug!("SMTP C (pipelined): MAIL FROM + {} RCPT TO", recipients.len());
+    stream.write_all(batch.as_bytes()).await?;
+    stream.flush().await?;
+
+    // Read MAIL FROM response
+    let mail_resp = read_response(stream, timeout_secs).await?;
+    if !mail_resp.is_success() {
+        return Err(mail_resp.to_error());
+    }
+
+    // Read RCPT TO responses
+    let mut accepted = Vec::new();
+    let mut rejected = Vec::new();
+    for rcpt in recipients {
+        match read_response(stream, timeout_secs).await {
+            Ok(resp) => {
+                if resp.is_success() {
+                    accepted.push(rcpt.clone());
+                } else {
+                    rejected.push(rcpt.clone());
+                }
+            }
+            Err(_) => {
+                rejected.push(rcpt.clone());
+            }
+        }
+    }
+
+    Ok((true, accepted, rejected))
+}
+
 /// Send DATA command, followed by the message body with dot-stuffing.
 pub async fn send_data(
     stream: &mut ClientSmtpStream,