Typically refers to an email server (SMTP server) that is configured to deliver any incoming mail to another mail server. In the past, open relays (open relay servers) were common, but today, most email servers block all email that does not originate with the customers of the service or employees of the company. The term may also apply to a proxy server that can be used by the general public. See spam relay and anonymous remailer.
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. MarketingSherpa, Inc. The Ultimate Email Glossary: 180 Common Terms Defined. [Online, 2004.] MarketingSherpa, Inc. Website. http://www.marketingsherpa.com/ sample.cfm?contentID=2776.