Reliability of DNSBLs for Stopping Forum Spam

Question

I know that certain DNS blacklists are considered more reliable than others, in that they don't have as many false positives.

I run a forum that is known to be spammed, and I've installed a mod to incorporate multiple DNSBL lookups with varying weights in order to have less false-positives by confirming there are multiple DNSBLs confirming that IP address.

Is there a reliable list of recommended DNSBLs or a way to decide which ones to use? Are there well-known DNSBLs that return so many false positives they should be avoided?

Answer 1

Though my answer isn't to use DNSBL, there are services that provide an API-level plugin to help reduce spam for such use cases. Defensio is one that comes to mind. I'm sure there are others out there (and no, I don't work for Websense). Depending on the volume of posts per month, such services could be available for "free." With that said, many DNLBLs also limit the number of requests per day.