Real-time blackhole list. This differs from a blackhole list in that it actively boycotts TCP/IP addresses known to send spam or host spammers. Enabling such a list results in all mail from those addresses being refused, including valid email. This can, however, result in innocent users complaining to their ISPs and those ISPs enacting stronger anti-spam measures in order to get the RBL ban lifted.
Real-time Blackhole List, a MAPS service for blocking electronic mail from rogue mail relays.
Real-time Black List. A publicized list of IP addresses known to be sources of spam, which can be used to create a network blacklist to filter out mail originating from these addresses. (See dnsBL.)