Document 'message-send-mail-function' in the Emacs manual

Most of the manual here addresses Message mode, yet talks about
'send-mail-function' which is used for Mail mode.
Fixing this completely requires more involved work, but for now at
least document the difference here.

* doc/emacs/sending.texi (Mail Sending): Mention
'message-send-mail-function'.  (Bug#39639)

diff --git a/doc/emacs/sending.texi b/doc/emacs/sending.texi
index 246d6052e08d2a3838242236ab4194fec9434a75..8d3f96139ffe027fa7b0aa4ecdf20d9eab3ccd34 100644 (file)
--- a/doc/emacs/sending.texi
+++ b/doc/emacs/sending.texi
@@ -361,9 +361,12 @@ twice).
 @cindex Feedmail
 @cindex Sendmail
 @cindex Mailclient
+@vindex message-send-mail-function
 @vindex send-mail-function
-  The variable @code{send-mail-function} controls how the message is
-delivered.  Its value should be one of the following functions:
+  The variable @code{message-send-mail-function} controls how the
+message is delivered (@code{send-mail-function} is used for Mail mode).
+The value of @code{send-mail-function} should be one of the following
+functions:
 
 @table @code
 @item sendmail-query-once