Improve sendmail-program doc string

* lisp/mail/sendmail.el (sendmail-program): Document that the
program shouldn't output text (bug#56855).

diff --git a/lisp/mail/sendmail.el b/lisp/mail/sendmail.el
index f985b2ceac45ea04a8f5206e1a351f7b5cd2cbf3..189ad075c4770dd1f7ef82765a0cdc901c560bda 100644 (file)
--- a/lisp/mail/sendmail.el
+++ b/lisp/mail/sendmail.el
@@ -49,7 +49,9 @@
        ((file-exists-p "/usr/lib/sendmail") "/usr/lib/sendmail")
        ((file-exists-p "/usr/ucblib/sendmail") "/usr/ucblib/sendmail")
        (t "sendmail")))
-  "Program used to send messages."
+  "Program used to send messages.
+If the program returns a non-zero error code, or outputs any
+text, sending is considered \"failed\" by Emacs."
   :version "24.1"              ; add executable-find, remove fakemail
   :type 'file)