When sendmail processes one of the check_ rule sets (Section 7.1), and when that rule set rejects a message, sendmail logs the following message:

... ruleset=rset, arg1=firstarg, reject=reason

Here, rset is the name of the rule set called (such as check_mail, Section 7.1.2). The workspace passed to the rule set is indicated by firstarg. The reason for the rejection is echoed with the reject=reason. For example, the following rule causes mail to fax to be rejected:

Rfax                    $#error $@ 5.1.3 $: cannot send mail to fax

This rule would produce a reject= syslog(3) message such as this:

reject=553 5.1.3 <fax@ourhost>... cannot send mail to fax

A complete description of the construction of rejection messages can be found in Chapter 7.