The RBL is a list of IP addresses whose owners refuse to stop the proliferation of spam. Most mail server software can be configured to reject or flag messages which have been sent from a site listed on one or more such lists.

RBL was created in 1997 by Paul Vixie as part of his Mail Abuse Prevention System (MAPS). RBL falls under the general category of DNS-based Blackhole lists (DNSBLs) of which several exist. In recent years, a number of DNSBLs have come under denial-of-service attacks, probably by spammers pressuring the DNSBLs to shut down.