From: Lars Ingebrigtsen <larsi@gnus.org>
Date: Mon, 16 Sep 2019 21:45:34 +0000 (+0200)
Subject: Try resending when getting a transient 4xx SMTP code
X-Git-Tag: emacs-27.0.90~1551^2~28
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=603e70483b844201a46f13e0a9e7acf50d3fd273;p=emacs.git

Try resending when getting a transient 4xx SMTP code

* lisp/mail/smtpmail.el (smtpmail-via-smtp): Try resending when
getting a transient error message (bug#34177).
---

diff --git a/etc/NEWS b/etc/NEWS
index 12182694d1d..adb2b642ba9 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1162,6 +1162,10 @@ defining new 'cl-defmethod' of 'smtpmail-try-auth-method'.
 attempt when communicating with the SMTP server(s), the
 'smtpmail-servers-requiring-authorization' variable can be used.
 
+---
+*** smtpmail will now try resending mail when getting a transient 4xx
+error message from the SMTP server.
+
 ** Footnote mode
 
 *** Support Hebrew-style footnotes
diff --git a/lisp/mail/smtpmail.el b/lisp/mail/smtpmail.el
index f6fd1cd65eb..57913c1f0f0 100644
--- a/lisp/mail/smtpmail.el
+++ b/lisp/mail/smtpmail.el
@@ -654,10 +654,12 @@ Returns an error if the server cannot be contacted."
 	      user-mail-address))))
 
 (defun smtpmail-via-smtp (recipient smtpmail-text-buffer
-				    &optional ask-for-password)
+				    &optional ask-for-password
+                                    send-attempts)
   (unless smtpmail-smtp-server
     (smtpmail-query-smtp-server))
   (let ((process nil)
+        (send-attempts (or send-attempts 1))
 	(host (or smtpmail-smtp-server
 		  (error "`smtpmail-smtp-server' not defined")))
 	(port smtpmail-smtp-service)
@@ -819,6 +821,23 @@ Returns an error if the server cannot be contacted."
 	       ((smtpmail-ok-p (setq result (smtpmail-read-response process)))
 		;; Success.
 		)
+               ((and (numberp (car result))
+                     (<= 400 (car result) 499)
+                     (< send-attempts 10))
+                (message "Got transient error code %s when sending; retrying attempt %d..."
+                         (car result) send-attempts)
+                ;; Retry on getting a transient 4xx code; see
+                ;; https://tools.ietf.org/html/rfc5321#section-4.2.1
+                (ignore-errors
+		  (smtpmail-send-command process "QUIT")
+		  (smtpmail-read-response process))
+		(delete-process process)
+                (sleep-for 1)
+		(setq process nil)
+		(throw 'done
+		       (smtpmail-via-smtp recipient smtpmail-text-buffer
+                                          ask-for-password
+                                          (1+ send-attempts))))
 	       ((and auth-mechanisms
 		     (not ask-for-password)
 		     (eq (car result) 530))