HP-UX Mailing Services Administrator's Guide

Configuring and Administering Sendmail
Configuring Sendmail to Reject Unsolicited Mail
Chapter 288
Mail cannot be sent to [e-mail] or to anyone at
cyberspammer.com.
Realtime Blackhole List
This feature rejects hosts listed in the Realtime Blackhole List, which is
found in the Realtime Blackhole List server. The server is
blackholes.mail-abuse.org.
To use this feature, you must add the following line to the DNS database:
1.5.5.192.blackholes.mail-abuse.org IN A 127.0.0.2
You can specify the Realtime Blackhole List servers in the sendmail.cf
file.
Checking Headers
With header checking, you can reject mail messages based on the
contents of their mail headers. Sendmail provides the syntax for limited
header syntax checking. A configuration line of the form: HHeader:
$>Ruleset causes the specified ruleset to be invoked on the header when
read. Following is an example of header checking:
Validity of a Message-ID: header
#LOCAL_RULESETS
HMessage-Id: $>CheckMessageId
SCheckMessageId
R<$+@$+> $@OK
R$* $#error $: 553 Header Error
If the previous lines are included in the sendmail.cf file, then all header
messages of the form Message-Id: will call the ruleset
SCheckMessageID, which checks for the validity of the Message-Id
header.
Discard Mailer
Sendmail has defined a special internal delivery agent called discard.
You can use this agent with the header-checking ruleset and check
rulesets: check_mail, check_rcpt, check_relay, or check_compat.
If any of the check rulesets (check_mail, check_rcpt, check_relay, or
check_compat) or the header-checking ruleset resolves a mail address to
the $#discard mailer, then all the SMTP commands are accepted, but