So I would suggest offering SMTP (AUTH) support on
ports 25 and 26, just to
be sure.
No no no.
RFC: 2476:
| 3. Message Submission
| 3.1. Submission Identification
|
| Port 587 is reserved for email message submission as specified in
| this document. Messages received on this port are defined to be
| submissions. The protocol used is ESMTP [SMTP-MTA, ESMTP], with
| additional restrictions as specified here.
|
| While most email clients and servers can be configured to use port
| 587 instead of 25, there are cases where this is not possible or
| convenient. A site MAY choose to use port 25 for message submission,
| by designating some hosts to be MSAs and others to be MTAs.
Port 587 has been widely deployed:
$ telnet smtpauth.bluewin.ch 587
$ telnet
mail.gmx.net 587
$ telnet
smtp.gmail.com 587
Inventing new ports < 1024 is just plain wrong.
--
RFC 1925:
(11) Every old idea will be proposed again with a different name and
a different presentation, regardless of whether it works.