code: def send_to_queue(self, message):
          
          if not self.queue_delivery:
              raise RuntimeError("No queue_path provided")
  
          return self.queue_delivery.send(*self._message_args(message))
docs: Add a message to a maildir queue.
  
          In order to handle this, the setting 'mail.queue_path' must be
          provided and must point to a valid maildir.
  
          :param message: a 'Message' instance.