We've just gotten to the point that we use three (reputable) RBLs, and reject connections if they show up in any of them. About once a month, I have to whitelist a mail server (a client or vendor), but I let them know that they were in a black list and point them towards it so they can fix it (or find a new mail provider). It's reduced our spam (we have about 500 mailboxes) by about two thirds.

We're investigating other filter possibilities. Anyone have good results with any content filters? It seems the spammers change content faster than the filters can keep up.

-jk