Another non-perl solution: www.mailfrontier.com

They have a downloadable app which automatically challenges any mail sent to you. If the sender doesn't respond to the challenge, the mail is deleted, and you aren't bothered. If they do respond (correctly), their address is placed on a "white list", and all future mail gets right through. It works really well.

In all fairness, I must say that one of Mailfrontier's founders is a freind of mine, but no kidding, their software works great.

-Logan
"What do I want? I'm an American. I want more."