What is mail relay and why do I need to protect my Merak server from relaying?
Relaying is a mail transfer mechanism in which an intermediate SMTP server, a relay, is used to deliver mail from a source SMTP server to the destination SMTP server. The primary purpose of a mail relay server is to pass mail between different networks. Most commonly relaying is used to move mail between company’s publicly visible and private SMTP servers. One property of a relay server is that it hides the identity of the originating SMTP server from the destination SMTP server. This property is well known and widely abused by spammers, who use misconfigured third-party SMTP servers to send out millions of spam messages and often get away with it. Here is how it works: • Spammers run network scanners to identify live SMTP servers (i.e. anything that is listening on the port 25) • All found servers are tested whether they can be used to forward messages to domains other than their primary domain • Those servers that support relaying are chosen to deliver spam mail to the destination SM
