Sends the messages which have previously been queued into QueueDir .
This method sends the messages which have previously been queued into QueueDir. The PITrail event shows the interaction with the server as messages as are processed.
This method looks in the directory for files with extension ".queued" and starts processing them.
When processing starts, the file extension is changed to ".sending". If an error happens at this stage, the sending process is aborted, and the file extension is changed to ".failed".
If the file is successfully sent, the file is normally deleted, unless the KeepQueue configuration setting is set to True, in which case the file extension is instead changed to ".sent" and the queue file is not deleted.