Installing and Administering Internet Services

Chapter 4 201
Installing and Administering sendmail
Configuring sendmail to Reject Unsolicited Mail
mail through your site.
Relay Entire Domain: Relaying from Any Host in the Domain
By default only hosts listed as RELAY in the Access Database are
allowed to relay messages. The hosts must be defined in the m class ($=m)
macro to relay. However, this feature allows any host in your domain to
relay mail messages.
Relay Hosts Only: Relaying From Hosts Only
By default, host names that are listed as RELAY in both the Access
Database and the class ’R’ ($=R) macro can relay messages. When using
this feature, specify hostnames. This feature enables Sendmail tolook up
individual host names and relay messages to the host.
Relaying Based on MX Records
This feature allows relaying based on the MX records of the host portion
of an incoming recipient. If a MX record for host foo.com points to your
site, you will accept and relay mail addressed to foo.com.
Relay From Local
With this feature, a sender, who is a valid user on a particular host, can
relay messages to other users on different hosts.
Caution: Use caution when using this feature. Using it opens a window
for spammers. Specifically, spammers can send mail to your mail server
that claims to be from your domain (either directly or via a routed
address), and your machine will relay it out to any hosts on the Internet.
Check Loose Relay
This feature will turn off the default behavior, which rechecks all
recipients using "%" addressing. For example, if the recipient address is
user%site@othersite, and othersite is in class ’R’ macro, the
@othersite portion is stripped and re-checks user@site for relaying.
Validating Senders
Sendmail provides a stricter check of mail message senders to ensure
they are legitimate. Sendmail will refuse mail if the MAIL FROM:
parameter has an unresolvable domain. You can work around this. If you
want to continue accepting mail from such domains, use the features