Mail Abuse Prevention System

The Mail Abuse Prevention System (MAPS) is an organisation that provides anti-spam support by maintaining blacklists. They provide five blacklists, categorising why an IP address or an IP block is listed:


 * Real-Time Blackhole List (RBL), the one for which MAPS is probably best known.
 * Dialup Users List (DUL), blocks of IP addresses that include many small office and home office users.
 * Relay Spam Stopper (RSS), spam relays, e.g. hijacked servers.
 * Open Proxy Servers (OPS), naively open SMTP servers.
 * Non-confirming Mailing List (NML), marketers who use opt-out strategy.

The acronym MAPS is spam spelled backwards.