sendmail, 4th Edition

check_data

Check just after DATA Policy rule set

The check_data rule set can be used to validate recipients after all recipients have been declared with SMTP RCPT To: commands. Other uses for the check_data rule set include screening a combination of sender and recipient, and evaluating connection-based information.

The check_data rule set is called from inside sendmail just after the SMTP DATA command is received, but before that command is acknowledged:

RCPT To: <[e-mail]>
250 2.1.5 <[e-mail]>... Recipient ok
DATA
                                                       ← called here
354 Enter mail, end with "." on a line by itself       ← usually acknowledged here

The workspace passed to the check_data rule set is a count of the number of envelope recipients—that is, the number of accepted SMTP RCPT To: commands. One use for this rule set might be to reject messages that specify too many envelope recipients. Consider the following mc configuration lines:

LOCAL_CONFIG
Kmath arith

LOCAL_RULESETS
Scheck_data
R $-            $: $(math l $@ 19 $@ $1 $)       # reject >=20 envelope recipients
R FALSE         $# error $@ 5.7.1 $: "550 Too many recipients"

Here, we add two new sections to our mc configuration file. The first, under LOCAL_CONFIG, defines a database map of type arith (arith on page 898).

In the second section, following the LOCAL_RULESETS, we declare the check_data rule set. That rule set is followed by two rules. The first rule looks up the workspace (the LHS $-) that contains a count of the envelope recipients. The RHS of that rule looks up that value ...