But seriously, while I'm not having a giant spam problem in my filtered folders, I was having to search through a ton of spam in my unfiltered folder to find a the occasional legit message.
Of course, it was a few stupid things I did.
Each pair account comes with a default mailbox and a default address. Mine is "firstname.lastname@example.org." I never use it. I never publish it. Spammers send to it, though. To make things worse, that address bypasses my procmail filtering, so it just dumps mail into my default inbox (that I don't actually use for anything real, it's my "unfiltered" folder). I went in and set that address to discard mail; there should be absolutely nothing legitimate going to it.
I had an old address, "email@example.com." It forwards to my webmaster address. I don't have access to the account anymore, so if there's a .forward I can't remove it myself. I've not been able to get the owners of that service to remove the alias. I put in a procmail recipe to discard these messages, but as it turns out other recipes were tripping first, and they were just dropping into my default inbox (that I don't actually use). I rearranged my rules so this one would trip first, so there's a big chunk of spam gone.
I set my "junk" tagging to trigger on anything higher than a SpamAssassin "3" score. I set my auto-discard rule to trip on anything over a SpamAssassin "8" score. I get very little spam that scores less than 15. I may have some mail that's incorrectly flagged, but it should drop into a folder with much less crap amongst from to pick it out.