When the queues are processed normally, sendmail will attempt to deliver all messages (except those that have a recipient address that resolves to a delivery agent with the F=% flag (F=%) set). No distinction is made between recently queued messages and messages that have been in the queue for a long time.

Some sites might prefer to process the queue often—say, once every five minutes. This ensures that all important mail will be delivered promptly but can exact a price in degraded performance. Every time the queue is processed, sendmail tries to deliver every mail message in the queue, but many sites have queued messages that should not be retried every five minutes. One way to handle this problem is to set the MinQueueAge option. If it is set to 1h (one hour), every queued message is forced to remain in the queue for a minimum of one hour, even if the queue is processed more frequently. The forms of this option are as follows:

O MinQueueAge=wait                      configuration file (V8.7 and later) 
-OMinQueueAge=wait                      command line (V8.7 and later) 
define(`confMIN_QUEUE_AGE',`wait')      mc configuration (V8.7 and later) 

The argument wait is of type time. If wait is less than or equal to zero, or if it is missing, this feature is disabled. If the units in the time expression are omitted, the default is minutes. There is no default for the mc configuration method.

Note that the decision to process is not based on the time the message was placed into the queue. It is instead based on the time the message was last processed from the queue. This time is stored in the K line of the qf file (K line). This minimum is enforced only if the number of times delivery has been attempted is greater than zero (the qf file's N line, N line). This ensures that the first delivery attempt will be made immediately.

The MinQueueAge option is safe. If specified from the command line, sendmail will not relinquish its special privileges.