When a message begins life and delivery has not yet been attempted, the message is considered to have had zero delivery attempts. If the first delivery attempt fails, the message is deferred to the queue and marked as having had one delivery attempt. Thereafter, each time the message is fetched from the queue and delivery fails, the number of attempts is incremented. Each time the message is read from the queue, the number of delivery attempts is stored in the ${ntries} macro.

One use for this ${ntries} macro might be to bounce high-priority mail that fails on the first try. If it cannot be sent right away, perhaps such mail should be faxed, or followed up with a telephone call. Consider the following mc file lines that suggest one way to accomplish this:

LOCAL_CONFIG
C{persistentMacros} {X-Notice}
HX-Notice: $>CheckNotice
Kstore macro

LOCAL_RULESETS
SCheckNotice
R $*           $: $(store {X-Notice} $@ YES $)

Scheck_compat
R $*           $: $&{X-Notice}
R $*           $: $(store {X-Notice} $) $1
R YES          $: $(math l $@ $&{ntries} $@ 1 $)
R FALSE        $#error $@ 5.7.1 $: "550 X-Notice mail exceeded allowed tries"

Here, we set up our own ${X-Notice} macro as a private flag so that we can detect the presence of the X-Notice: header, even when the message is read from the queue. Under LOCAL_CONFIG, we first add the ${X-Notice} macro to the class $={persistentMacros} ($={persistentMacros}) which ensures that ${X-Notice} will retain its value despite the message being queued. We then use the H configuration command to define the X-Notice: header and to specify that the X-Notice: header's value must be processed by the CheckNotice rule set. Finally, we declare a macro type database map (macro) which we will reference with the name store.

In the LOCAL_RULESETS section we set up two rule sets. The first rule set is the CheckNotice rule set we referenced with the H configuration command. That rule set contains a single rule which stores a literal YES into the ${X-Notice} macro.

The second rule set is the check_compat rule set (Section 7.1.4), which is called just prior to delivery. It contains four rules. The first rule fetches the current value (the $&) of the ${X-Notice} macro and places that value into the workspace. The second rule clears the ${X-Notice} macro to ready it for any future message. The third rule looks for a literal YES in the workspace, and if found, compares the value in the ${ntries} macro to a one. If ${ntries} is not less than one, a literal FALSE is placed into the workspace. The last rule looks for a literal FALSE in the workspace, and if found, rejects (bounces) the message with an appropriate notice.

${ntries} is transient. If it is defined in the configuration file or in the command line, that definition can be ignored by sendmail. Note that a $& prefix is necessary when you reference this macro in rules (that is, use $&{ntries}, not ${ntries}).