just wanted to introduce a good way to fight spam on server-level, it's called greylisting. I have set it up on my new server and it's working really fine!
now, what is greylisting?
it's a VERY simple but effective technique that exploits the fact that most spammers send mails the hit&run way: they send it and don't care if it was delivered or not...it's the pure amount that counts, so they don't care about single addresses.
and that's where greylisting do it's job: every regular email is sent, and when the mail server of the recipient is busy or down it tries later again....depending on the configuration of the sender's mail server it can even try for days to deliver it. when greylisting is in effect the sending mail server simply gets a "not now, try again in xx minutes" answer from the recipient mail server....every "friendly" mail server has no problem with that and tries again later, but spam servers don't.
the only negative aspect is that a user has to wait the greylisting time in order to get his email...but 5 minutes is usually already enough already (the longer the more effective greylisting is).
greylisting for Postfix:
http://postgrey.schweikert.ch/
for exim:
http://slett.net/spam-filtering-for-mx/ ... sting.html