In general, implementing an RBL provides the most immediate benefit to reducing spam traffic. A good RBL implemented by your MTAs immediately reduces spam by a minimum of 10 percent. In some cases, this number could approach 50 percent.
You can use your RBL and Brightmail together. If Brightmail takes care of 95 out of 100 emails for a certain IP address within some amount of time you should add that IP address to your RBL. You can adjust the RBLs for Brightmail’s false positives when you do your Brightmail analysis. That makes the RBL much more proactive in handling a specific wave of spam.