Allow specifying that SMTP auth should always be used

* doc/misc/smtpmail.texi (Authentication): Document it.

* lisp/mail/smtpmail.el
(smtpmail-servers-requiring-authorization): New variable (bug#26359).
(smtpmail-via-smtp): Use it.

1 files changed, 11 insertions, 3 deletions

diff --git a/doc/misc/smtpmail.texi b/doc/misc/smtpmail.texi
index 365f55718e7..b2fc90a337a 100644
--- a/doc/misc/smtpmail.texi
+++ b/doc/misc/smtpmail.texi
@@ -221,10 +221,18 @@ they are allowed to send mail.  Authentication usually involves
 supplying a user name and password.
 
 If you have not configured anything, then the first time you try to
-send mail via a server, Emacs (version 24.1 and later) prompts you
+send mail via a server and the SMTP server reports back that it
+requires authentication, Emacs (version 24.1 and later) prompts you
 for the user name and password to use, and then offers to save the
-information.  By default, Emacs stores authentication information in
-a file @file{~/.authinfo}.
+information.  By default, Emacs stores authentication information in a
+file @file{~/.authinfo}.
+
+@vindex smtpmail-servers-requiring-authorization
+Some SMTP servers may bandwidth-limit (or deny) requests from clients
+that try to post without authorization---even if they later do supply
+that information.  To make this library supply that information on
+first attempt, set @code{smtpmail-servers-requiring-authorization} to
+a regexp that match the server name.
 
 @cindex authinfo
 The basic format of the @file{~/.authinfo} file is one line for each