To limit the amount of time a message can remain in the queue before being bounced, sendmail must know when that message was first placed in the queue. That time of first placement is stored in the T line in the qf file. For example, the following number represents the date and time in seconds since January 1, 1970:

T703531020

Each time sendmail fails to deliver a message from the queue, it checks to see whether too much time has passed. It adds the T line value to the value specified in the Timeout.queuereturn option (Timeout). If that sum is greater than the current time, the message is bounced instead of being left in the queue.

Messages are occasionally left in the queue for longer than the normal timeout period. This might happen, for example, if a remote machine is down but you know that it will eventually be brought back up. There are two ways to lengthen the amount of time a message can remain in the queue.

The preferred way is to create a temporary separate queue directory and move the necessary queued file to that temporary holding place. When the remote site comes back up, you can later process the files in that other queue by running sendmail with an artificially long Timeout.queuereturn value (Section 11.9).

A second way to extend the life of messages in the queue is to edit the qf file and change the value stored in the T line. Just add 86400 to that value for each day you want to extend. Care is required to avoid editing a file that is currently being processed by sendmail.^[14]

^[14] The nvi(1) editor uses the same file locking as sendmail and so can safely be used to edit qf files.

There is currently no plan to give sendmail the ability to rejuvenate queued messages (make old messages appear young).

The form of the T line in the qf file is:

Tsecs

The T begins the line, and the secs must immediately follow with no intervening space. The numeric text that forms secs is converted to an integer using the C-library routine atol(3). That routine allows secs to be represented in text as a signed decimal number, an octal number, or a hexadecimal number.

If secs is absent or the entire T line is absent, the time value is zero. A zero value causes the mail message to time out immediately.

There should be only one T line in any qf file. Multiple T lines cause all but the last to be ignored.