Milter-greylist

On 12/7/06, Oliver Fromme <olli@...> wrote:
> Now the problem:  There's a backup MX (secondary) whose
> sole purpose is to accept and spool mails if the primary
> MX is down for some reason, and then send the queued stuff
> to the primary when it's up again.  The secondary doesn't
> know about valis users on the primary, so it accepts _all_
> mails.  Most of them is spam or spam-probes to non-existing
> addresses.  (Spammers seem to prefer secondaries even if the
> primary MX is available ...  Maybe they think that on backup
> mail servers there are less anti-spam measures.  Or maybe
> they simply don't care about the MX priorities and send
> their crap to a random MX.)
>
> Of course, what happens is this:  As soon as the secondary
> tries to relay the mails to the primary, it gets a "user
> unknow" reply, which leads to a bounce message which is
> either sent back to innocent people (because of forged
> sender addresses) or stays in the mailq on the secondary
> for a long time (because the bounce cannot be delivered to
> the sender for various reasons).
>
> So the reuslt of the situation is that the secondary gets
> a huge mail queue which is full of bounces that never will
> be delivered (and expire after five days, generating post-
> master mails).  And furthermore, the seondary is sending
> lots of bogus delivery errors to innocent people.
>
> Is there a _simple_ solution to solve the problem?

Have you heard about the mailfromd sendmail milter?  I haven't used it
but it looks like it would do what you want.
http://puszcza.gnu.org.ua/projects/mailfromd/

Documentation:
http://gray.gnu.org.ua/software/mailfromd/manual/

It looks like it does what you want.  It seems to do the same thing as
milter-ahead but it is free software.

John