sendmail, 4th Edition

Periodically with -q

The -q command-line switch is used both to cause queues to be processed and to specify the interval between queue runs.

A typical invocation of the sendmail daemon looks like this:

/usr/sbin/sendmail -bd -q1h

Here, the sendmail program is placed into listening mode with the -bd command-line switch. The -q1h command-line switch tells it to process the queue once each hour. Note that either switch puts sendmail into the background as a daemon. The -bd switch just allows sendmail to listen for incoming SMTP connections. Consider the following:

/usr/sbin/sendmail -bd
/usr/sbin/sendmail -q1h

This runs two daemons simultaneously. The first listens for incoming SMTP connections. The second processes the queues once per hour.

The time expression following the -q is constructed from an integer followed by a letter. The letters and the meaning of each are listed in Table 11-5. Integer and letter groups can be combined—for example, 5d12h means 5 days, 12 hours. If a letter is missing, the default is minutes.

Table 11-5. Meaning of time letters

Letter	Meaning
w	Week
d	Day
h	Hour
m	Minute
s	Second

At small sites, where mail messages are rarely queued, the time interval chosen can be small to ensure that all mail is delivered promptly. An interval of 15m (15 minutes) might be appropriate.

At many sites, an interval of one hour is probably best. It is short enough to ensure that delays in delivery remain tolerable, yet long enough to ensure that queue processing does not ...