HP-UX Mailing Services Administrator's Guide

Configuring and Administering Sendmail
Configuring Sendmail to Reject Unsolicited Mail
Chapter 2 91
Sendmail Validation
The check_compat ruleset compares all sender and receiver pairs before
mail is delivered. It validates the mail based on the results of the
comparison. It checks to see if host A can legally send a message to host
B. check_compat is called for all mail deliveries, not just SMTP
transactions.
check_compat is used in the following situations:
• A set of users who are restricted from sending mail messages to
external domains need to send mail messages to internal domains.
Both the sender and recipient addresses are checked to ensure that
they are in the local domain.
• A particular user needs to ensure that he or she does not receive mail
messages from a specific source.
• A particular host needs to ensure that external senders do not use
that host as a a mail relay. The mail messages are screened based on
the sender’s host name.