Timeouts and Intervals

Timeouts and Intervals

Time intervals use the following abbreviations:

s: seconds
m: minutes
h: hours
d: days
w: weeks

For example, "10m" represents 10 minutes, and "2h30m" represents two hours and 30 minutes.

Queue Interval

The argument to the -q flag specifies how often to process the mail queue. When the sendmail daemon is started with the /etc/init.d/mail script, the queue interval is set to 15 minutes.

If sendmail runs in delivery mode b, messages are written to the queue only when they cannot be delivered (for example, when a recipient host is down). Therefore, the need to process the queue is limited and the queue interval value may be set quite high. The value is relevant only when a host that was down comes back up.

If sendmail runs in delivery mode q, the queue interval should be set to a low value, as it defines the longest time that a message sits in the local queue before being processed.

Read Timeouts

sendmail can time out when reading the standard input or when reading from a remote SMTP server. Technically, a timeout is not acceptable within the published protocols. However, setting the read timeout option to a high value (such as an hour) reduces the chance that a large number of idle daemons will pile up on a system. The read timeout option is r.

Message Timeouts

sendmail causes a queued message to time out after a specified time period. This feature ensures that the sender knows the message cannot be delivered. This default message timeout value is one week (seven days). The value is set with the T option.

The queue records the time of submission, rather than the time remaining until timeout. This approach enables sendmail to flush messages that have been hanging for a short period by running the queue with a short message timeout. The following example illustrates how to process the queue and flush any message that is one day old:

/usr/lib/sendmail -oT1d -q