Outbound and Inbound mail on same server

David Sullivan David.Sullivan at BARNET.AC.UK
Tue Feb 4 17:45:31 GMT 2003

On 4 Feb 2003 at 12:12, Randy Herban wrote:

> Background:
> 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.

Relevant section of the manual:


The section mentioning resource usage is probably less of a problem
now since caching for these callouts was included in 4.11 but the
documentation has not yet been updated.

If you're then not accepting these messages to users that don't exist
and not scanning them or trying to send bounce messages this might
resolve some loading issues.



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