RHSBL
From Wiki.openrbl.org
Right-Hand Side or Hostname-based lists
Go to:
Commonly refered to as DNSBL.
Lookup done by Fully.Qualified.hostname,
Example for fictious zone rhsbl.example.com:
host.example.com -> host.example.com.rhsbl.example.com
most hostname-based blocklists may be used with content filters like SpamAssassin

