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3 If you want, log the packets to monitor the SMTP abuse.
4 Add more lters for the SMTP port to allow or deny access from other IP addresses
or address ranges.
For additional information about Firewall service, see Network Services Administration.
Limiting Junk Mail and Viruses
You can congure Mail service to decrease the volume of unsolicited commercial mail,
also known as junk mail (or spam), and mail containing viruses. You can take steps to
block junk mail or viruses that are sent to mail users. Additionally, you can secure your
server against use by Mail service abusers who try to use your resources to send junk
mail to others.
You can also take steps to prevent senders of junk mail from using your server as
a relay point. A relay point or open relay is a server that unselectively receives and
forwards mail addressed to other servers. An open relay sends mail from any domain
to any domain.
Junk mail senders exploit open relay servers to avoid having their SMTP servers
blacklisted as sources of junk mail. You don’t want your server blacklisted as an open
relay because other servers might reject mail from your users.
There are two main methods of preventing viruses and junk mail passing through or
into your mail system. Using both methods helps mail system integrity. The two points
of control are explained in the following sections:
“ Â Connection Control” on page 34
“ Â Mail Service Filtering” on page 35
Connection Control
This method of prevention controls which servers can connect to your mail system
and what those servers must do to send mail through your mail system. Your Mail
service can do any of the following to exercise connection control:
Require SMTP authentication. See “ Â Requiring SMTP Authentication” on page 27.
Restrict SMTP relay, allowing relay only by approved servers. See “ Â Restricting SMTP
Relay” on page 31.
Reject all SMTP connections from disapproved servers. See “ Â Rejecting SMTP
Connections from Specic Servers” on page 32.
Reject mail from blacklisted servers. See “ Â Rejecting Mail from Blacklisted Senders”
on page 33.
Filter SMTP connections. See “ Â Filtering SMTP Connections” on page 33.
34 Chapter 2 Mail Service Setup