)
Spammers often deliver their annoying messages from a normal dial-up Internet account. They
need some kind of high-capacity e-mail server to accept and buffer the payload of messages. They
deliver the spam to the server all in one huge batch and then log off, letting the server do the work
of delivering the messages to the many victims.
Naturally, no self-respecting Internet service provider will cooperate with this action, so spammers
resort to hijacking servers at another ISP to do the dirty work. Having your mailserver hijacked to
act as a spam relay can have a devastating effect on your system and your reputation. Fortunately,
open mail relaying is deactivated by default on Fedora and Red Hat Enterprise Linux installations.
Open mail relaying is one security issue that you will not have to worry about.
You can allow specific hosts or domains to relay mail through your system by adding those senders
to your /etc/mail/access file with keyword RELAY. By default, relaying is allowed from the
local host only.
One package you might consider using to filter out spam on your mail server is
SpamAssassin. SpamAssassin examines the text of incoming mail messages and attempts
to filter out messages that are determined to be spam. SpamAssassin is described in Chapter 25.
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