An SMTP email server permitting outsiders to relay email not for or from local users. Spammers rely on open relay to send unwanted messages to potential consumers. Open relays are blacklisted by some Internet services, and other mail servers use these lists to block emails from the open relay servers. System administrators of open relays are contacted by the listing service asking them to fix their configurations in order to be removed from the black list.

See Also: Administrators; Electronic Mail or Email; Internet; Simple Mail Transfer Protocol (SMTP); Spam; Spammers.