def enqueue(self, message, *, delay=None):
        """Enqueue a message.

        Parameters:
          message(Message): The message to enqueue.
          delay(int): The minimum amount of time, in milliseconds, to
            delay the message by.

        Raises:
          QueueNotFound: If the queue the message is being enqueued on
            doesn't exist.
        """
        queue_name = message.queue_name
        if delay is not None:
            queue_name = dq_name(queue_name)
            message_eta = current_millis() + delay
            message = message.copy(
                queue_name=queue_name,
                options={
                    "eta": message_eta,
                },
            )

        if queue_name not in self.queues:
            raise QueueNotFound(queue_name)

        self.emit_before("enqueue", message, delay)
        self.queues[queue_name].put(message.encode())
        self.emit_after("enqueue", message, delay)
        return message