Measures reported by DropQueueTest

Messages that have been submitted via the Postfix sendmail command, but not yet brought into the main Postfix queue by the pickup service, await processing in the maildrop queue. Messages can be added to the maildrop queue even when the Postfix system is not running. These messages will be processed only after the Postfix is started. All mails that enter the Postfix queue have to pass through the cleanup service which is responsible for envelope and header rewriting, header and body regular expression checks, automatic bcc recipient processing, milter content processing, and reliable insertion of the message into the incoming queue.

Since the pickup service is single threaded, only one message can be delivered at a time at a rate that does not exceed the disk I/O latency of the cleanup service. If the cleanup service consumes excessive CPU or if the queue is nearly full or if the local message submission rate is high in the maildrop queue, then it indicates congestion of the queue. Also, if the active queue is full, the pikup service may slow down the message injection to the active queue which may also lead to the congestion of the maildrop queue. If the maildrop queue is congested for a longer duration, then new mails may not be accommodated to the queue resulting in slowdown in the reception of mails by the Postfix server. To avoid frequent congestion of the maildrop queue and to figure out the domain to which a large number of messages have arrived in the maildrop queue, administrators can use the DropQueueTest.

This test periodically monitors the maildrop queue of the target Postfix mail server and reports the total size of the queue as well as the split up of the message count in terms of time duration i.e., the number of messages that were in the queue for a specified time duration.

The measures made by this test are as follows: