What is RBL?
RBL stands for Realtime Blackhole List, this is a term for DNS based systems designed to assist in the prevention of email abuse. The first such system was created by Mail Abuse Prevention System (MAPS) LLC who have been granted a Service Mark for the term. The generic name for wsuch services is DNSBL.
The DNSBL consists of a DNS based system containing lists of IP addresses whose owners refuse to stop the proliferation of spam whether this be by running their mail servers as open relays, or by allowing their dialup users free outbound access to port 25.
As subscribers to the DNSBL, ISPs and companies will know from which IP addresses to block traffic. Most traffic blocking occurs during the SMTP connection phase. The receiving end will check the DNSBL for the connecting IP address. If the IP address matches one on the list, then the connection gets dropped before accepting any traffic from the spammer.
Some ISPs, though, will choose to blackhole (or disallow) IP packets at their routers. The goal here is to block all IP traffic.
Using Gordano's product GMS Anti-Spam an incoming connection is dynamically checked to see if it is blacklisted at any RBL Server, transactions can be rejected either at the connection stage or at the MAIL protocol stage. For further information on GMS Anti-Spam click here.