This section will discuss the various methods Postfix provides to help stop unwanted messages. Spam, or unsolicited commercial e-mail, is perhaps the biggest problem that e-mail server administrators face, but there may also be other kinds of messages that one does not want to receive.
Postfix by itself will not stop all spam, but it can catch many spam messages. For some people this may be adequate, but if you need to fight large volumes of spam you may need a tool such as SpamAssassin, described in Chapter 8. Even if you use SpamAssassin, Postfix's own lightweight methods can help reduce the load on the server by rejecting the messages before they even reach SpamAssassin.