[Mailman-Users] Google mail servers reply "Multiple destination domains per transaction is unsupported "

Stephen J. Turnbull stephen at xemacs.org
Sat Mar 9 19:25:43 CET 2013

Joseph Brennan writes:
 > "Stephen J. Turnbull" <stephen at xemacs.org> wrote:
 > > I bet they think it's an anti-spam measure.  None of the big services
 > > likes to talk much about that.
 > That's what frontline helpdesk told me, but no one could explain how
 > it reduces spam.

Rich man's graylisting, is my guess.  Many spammers never come back
for the remaining domains, I bet.

 > It beats me why, say, 6 recipients at one domain is less spammy
 > than 6 recipients at two domains.

It isn't.  3 recips at one of two domains is less spammy than 6 recips
at both domains, though!

 > We run our own smtp servers. They determine where each user's mail
 > goes. Some users are on Google Apps, so we re-send their mail to
 > Google's MX address. That's when the fun begins.
 > What I demonstrated is what happens when any host anywhere connects
 > to Google's MX address and tries to send to addresses at two domains
 > both hosted by Google.

But I don't understand why a host would do that in the course of
ordinary mail processing, unless it is using Google's MX as a
smarthost.  Are you really buying anything by

(1) Looking up the MXes for all recips
(2) Grouping by MX
(3) Batching to each MX in the list


Smarthost is a special case, because the assumption is that the sender
doesn't know how to route, and all outgoing mail goes through the
smarthost.  But the smarthost case is what the submission protocol is
designed to address (and it requires authentication).

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