1. E-mail relay is where spammers hijack an e-mail server in order to forward their spam through the server. Usually, the spammer (from the Internet) sends the e-mail server a single e-mail with thousands of recipients. Similarly, any open USENET server can be hijacked to relay spam to newsgroups. Key point: This allows a spammer with a dial-up account to send e-mail as fast as a high-speed Internet connection, since it is the victim who breaks apart the recipient list and sends each person a separate copy. Therefore, one e-mail goes into the server, thousands come out. Key point: Relaying can be turned off in the e-mail server configuration. Such configuration will force the server to accept either incoming mail, or outgoing mail, but not incoming e-mail destined back out to the Internet. There are several sites on the Internet that will scan your corporate e-mail server to see if will relay spam. Key point: Some e-mail relays are completely open, others are closed to open relaying, but have bugs that can be exploited in order to relay spam. Resource: Paul Vixie's MAPS http://maps.vix.com/ (MAPS is SPAM spelled backwards). From Hacking-Lexicon