The Realtime Blackhole List (RBL) belongs to the DNS-based Blackhole Lists( DNSBL). The RBL list is a real-time list. It was introduced back in 1996, is constantly updated and can be accessed from the Mail Abuse Prevention System (MAPS) website. The RBL list is a basic protection against spam, which can be increased by the other MAPS lists.
The name Realtime Blackhole List (RBL) is a registered trademark of Trend Micro.