A Guide to Anti-Spam Software
Anti-spam software dates back to the mid-1990s, when two software engineers started compiling a list of IP addresses from which they had received unsolicited and unwanted emails. The list was distributed as a Border Gateway Protocol to subscribers of the “Mail Abuse Prevention System” (“MAPS” or “SPAM” spelled backwards), which later developed into the Domain Name Server Blackhole List.
More than twenty years later, the Domain Name Server Blackhole List (often called the Real-time Blackhole List or “RBL”) is still the primary mechanism used by anti-spam