Yeah... there's no real "tuning" options for spamassassin, at least not easy ones. You have to dig deep into the thing to figure out what particular tests are good "hits" for you, and then change the scoring values for each. Your best bet is looking at the X-Spam-Level flag in the headers, then you can match at some custom level above/below, rather than the simple default "Spam=yes" settings in the procmail file. Or, you can setup a custom spamassassin config file and tune anything, but as the new system is different, I think that's not worth the effort.
The new system will be ENTIRELY learning-based. It'll start off knowing nothing, and delivering mail to an "Unsure" folder. You can drag/drop (move) mail from there to "Spam" (where it will be learned as spam) or some other folder (like the inbox) where it will be learned as non-spam. As it learns, it'll start putting detected spam into the Spam folder directly, and it will be auto-deleted after 30 days. If you pull it out of there into another folder, it will correct the training. Ditto something it puts straight in the inbox that actually IS spam... just drop it in spam and it'll learn. I've been using this system for about 2 months on my personal account, and it's pretty accurate. Of course, as spammers come out with new tactics/spams, you'll probably get a few that slip through into "Unsure" but it quickly corrects itself based on your training. Usually when I get a new spam, one or two of them is all I have to train before it catches on.
I particularly like the idea of an "Unsure" folder. It provides a buffer for those near-misses, so it's a lot less likely to have a fully false positive. That means I can sort through only a few "unsures" for potential mistakes, rather than the entire spam folder. My admin email address is probably one of the worst case scenarios for spam filtering possible. It's a public address, used by hundreds of people, all in very different places in life. Thus, the emails I get range from professional inquiries from other system administrators, all the way down to requests to "plz giv me ur free site hosted thx" I get emails in other languages, with blank subjects, misspelled words, bad formatting, etc... all of which are still "legit." I've had one false positive since I started using this system, and it had more ads tagged onto the bottom by the "free" email service the sender used than most spam usually does.
