Open Relay Behavior-modification System

Open Relay Behavior-modification System (ORBS), created and run by Alan Brown in New Zealand, was one of the first DNS-based Blackhole Lists (DNSBL), a means by which an internet domain may publish a list of IP addresses, in a database which can be easily queried automatically by other computer programs on the Internet. The ORBS list was used to blacklist IP addresses that were open mail relays, third-party mail servers through which spammers can relay their messages and thus attempt to obfuscate the source of the spam.