Outbound and Inbound mail on same server

[Peter Peters]

On Tue, 4 Feb 2003 17:45:31 -0000, you wrote:

>> We support mail accounts for several tens of thousand customers.  The
>> majority of the mail we deal with is spam coming into our accounts
>> using dictionary attacks or the like. With this in mind, the majority
>> of the mail in the Outgoing queue at any time are MAILER-DAEMON
>> messages with bounce-backs of user unknowns tryin to send mail to a
>> host that doesn't accept mail.
>>
>If you're running a mail server that acts as a "gateway" mail server
>like this it might be worth looking at exim, I'm not intending to
>start an MTA war with such a comment but this is very easy to do with
>exim 4 acls which can reject a message at the SMTP stage if recipient
>callout checks determine that the address isn't valid. I don't
>believe that sendmail can do similar but I couldn't say for sure.

We do the address-account/host translation on our border mailgateway but
still we end up with thousands of bounces in the outgoing queue. The
problem is sendmail tries to do it "the right way". When somebody uses a
non-existant address we return a 5xx. Normally the other system would
respond with QUIT or something like that. But most spamware just
disconnects. So sendmail (and any other MTA) doesn't know whether the
sending MTA has ever received the 5xx. So he decides to report the
failure himself.

If it were only for the spamware I would clean this out, but there is
some MTA(-like) software that acts the same way. (and even MUA(-like)
software from the same vendor does it occasionally.

--
Peter Peters                        senior netwerkbeheerder
Centrum voor InformatieTechnologie, Bibliotheek en Educatie
Universiteit Twente, Postbus 217,  7500 AE  Enschede
telefoon: +31 53 489 2301, fax:+31 53 489 2383, http://www.utwente.nl/civ