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

... ruleset=rset, arg1=firstarg, discard
... 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.

Note that some check_ rule sets (such as check_relay, Section 7.1.1) take more than one argument. If so, the workspace is provided with the first argument separated from the second with a $| operator. When a second argument is supplied, the log lines shown earlier will have an arg2= equate added which shows that second argument.

When a message is rejected, a reason is passed back to the original envelope sender. That reason is echoed with the reject=reason (reject=).