Greylist scanning (may appear in OpenBSD 4.1)

Make use of that 30 minutes!

Use a blacklist if you can - spammers find their way into them.	greylist gives ttime for hosts to be blacklisted. but many of us can't

spamdb | script

Perl your way through your greylist. make your own decisions about what you see, and trap the ones you don't like.. This is very effective, as spammers have dirty sender and dirty recipient lists. 

While your MTA will reject a single message with a bogus recipient or sender, trapping a spammer in the greylist when sending one of those along with a thousand others gets rid of all thousand messages.

Spam senders often also have a recognizable sending profile - coming from many domains, etc.