Each time delivery is attempted for a message, the number stored in its qf file's N line is incremented by one. This number always begins at zero.

When delivering many messages to a single host, sendmail remembers failures. If one message fails to make it all the way through an SMTP dialog, all the following messages to that same host will be deferred (not attempted during the current queue run). For those deferred messages the number of tries is correctly incremented as though the delivery was actually attempted.

The value in this N line is used to determine whether the delay of the MinQueueAge option (MinQueueAge) should be triggered. This value, when zero, can also be used to enable a special first-time connection timeout (See this section).