I don't have anything Perlish to add, other than a hearty 'amen' to the previous suggestions. However, if you're running sendmail and wanting to use SpamAssassin, you'll need a milter. My office has been using spampd with good results. The author, Maxim Paperno, has also been very helpful in assisting me track down what few problems we have had.

I'm not affiliated with spampd, Paperno, or his employer. Just trying to help out where I can.

If things get any worse, I'll have to ask you to stop helping me.