> We've just started an email project at work and a comment that
> came from out internet connector (I don't know whether provider is
> quite the correct way to put it in our case) is that having a
> seperate incoming and a separate outgoing SMTP server is better
> security wise.
I agree with your ISP. I even use different machines for incoming
and outgoing mail. That way I can shut down the outgoing queue for
maintenance and still receive mail (and the other way round). If the
incoming queue should fill up, it would not affect outgoing mail.
Redundant queue setups further save me from having to have a backup MX.
Additionally, this setup allows to increase queue performance by adding
more machines (using DNS RR sets) to the queue that needs more throughput.
Exim supports such a setup via hosts_treat_as_local = "mx.domain" in
the configuration of the outgoing queue. You also need allow_localhost = true
in the transport on the outgoing queue that feeds mails back to the incoming
queue (e.g. bounces).
Michael
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