Queues the message into QueueDir .
def queue(queue_dir: str) -> str: ...
This method queues the message into QueueDir. The message is queued into a unique file into the directory QueueDir for future processing.
QueueDir must already exist, or an error will be generated.
The method returns the name of the unique queue file created in QueueDir. The file extension is ".queued".
Please refer to the process_queue method for more information on email queue processing.