How good is RBL at filtering spam?

[David Harris]

I'm thinking of deploying RBL to try to cut down on spam, but before I did that
I wanted to poke around and see how effective it might be. So, I gathered up
some spam messages that I had received and looked up the mailserver's ipaddr in
RBL using rbl.maps.vix.com and rbl.dorkslayers.com, and not one host was
rejected from either RBL site. Even though I could see the messages looked like
they were going trough an open relay.

How good is this whole RBL thing anyway?

 - David Harris
   Principal Engineer, DRH Internet Services