support DSN in sendmail.el

[Simon Josefsson <jas@extundo.com>]

This implements DSN support for sendmail.el, if the MTA can handle it.
I have not tested it at all, but it looks good.

Note :version "21.3" again.

2002-04-24  Simon Josefsson  <jas@extundo.com>

	* mail/sendmail.el (mail-use-dsn): New variable to request
	delivery status notification from MTA.
	(sendmail-send-it): Use it.

--- sendmail.el.~1.252.~	Wed Mar  6 19:42:59 2002
+++ sendmail.el	Wed Apr 24 22:31:31 2002
@@ -1,6 +1,6 @@
 ;;; sendmail.el --- mail sending commands for Emacs.  -*- byte-compile-dynamic: t -*-
 
-;; Copyright (C) 1985, 86, 92, 93, 94, 95, 96, 98, 2000, 2001
+;; Copyright (C) 1985, 86, 92, 93, 94, 95, 96, 98, 2000, 2001, 2002
 ;;   Free Software Foundation, Inc.
 
 ;; Maintainer: FSF
@@ -301,6 +301,16 @@
   :type '(choice (const t) (const nil) (const query) (const mime))
   :group 'sendmail)
 
+(defcustom mail-use-dsn nil
+  "*Ask MTA for notification of failed, delayed or successful delivery.
+Note that only some MTAs (currently only recent versions of Sendmail)
+support Delivery Status Notification."
+  :group 'sendmail
+  :type '(repeat (radio (const :tag "Failure" failure)
+			(const :tag "Delay" delay)
+			(const :tag "Success" success)))
+  :version "21.3")
+
 ;; Note: could use /usr/ucb/mail instead of sendmail;
 ;; options -t, and -v if not interactive.
 (defvar mail-mailer-swallows-blank-line
@@ -991,6 +1001,9 @@
 ;;;			      (or resend-to-addresses
 				  '("-t")
 ;;;				  )
+			      (if mail-use-dsn
+				  (list "-N" (mapconcat 'symbol-name
+							mail-use-dsn ",")))
 			      )
 		      )
 		     (exit-value (apply 'call-process-region args)))