[Mimedefang] Re: Postmaster, <>, and a Backup MX

[Troy Carpenter]

> Date: Thu, 30 Sep 2004 11:41:17 -0400 (EDT)
> From: "David F. Skoll" <dfs at roaringpenguin.com>
> Subject: Re: [Mimedefang] Postmaster, <>, and a Backup MX
> To: mimedefang at lists.roaringpenguin.com
> Message-ID:
> 	<Pine.LNX.4.58.0409301139370.6146 at shishi.roaringpenguin.com>
> Content-Type: TEXT/PLAIN; charset=US-ASCII
>
> {snip}
>
> The backup MX is violating a SHOULD requirement of RFC 2821:
>
>    All other types of messages (i.e., any message which is not required
>    by a standards-track RFC to have a null reverse-path) SHOULD be sent
>    with with a valid, non-null reverse-path.
>
> It seems like the backup MX is doing something similar to
> md_check_against_smtp_server.  It should use the real MAIL FROM: address,
> not <>, to perform this check.
>
> Regards,
>
> David.
>

Well, like you said, this is a SHOULD, not a MUST.  And as someone who
makes products compliant to international specifications, there is a big
difference between SHOULD and MUST (most of us shoot for, but never quite
implement the SHOULDs).

This is a backup MX that I have no control over.  I actually discovered it
when I was investigating my sendmail logs.  Anytime my server received an
email from my backup MX, I would see a lone entry similar to this
(modified, of course):

from=<>, size=0, class=0, nrcpts=1, proto=SMTP, daemon=MTA,
relay=mailnull at mybackupmx.com [220.169.132.45]

After playing around with a telnet session and the backup MX, I figured
out what it was doing.  Whenever I did a "rcpt to:" command on the backup
MX, that log above would appear.

Truthfully, I don't really care how they are doing it, as long as I
understand how it impacts my system.

Troy Carpenter
troy at carpenter.cx