I gave up on spam filters a few years ago and use the simple trick of sending all incoming mail via googlemail and letting them do the spam filtering. I forward the mail on the server to a googlemail address and then collect the filtered mail from googlemail using pop or IMAP, Macs usually prefer IMAP.

I've used this technique for quite a few people and found googlemail much more responsive to changes in spam techniques than any filters on my own system.

No need to limit yourself to text only emails or receiving mail only form addresses in your addressbook. These are ancient techniques that are no longer necessary and far too restricting.

Simon