public function queue(Queue $queue)
    {
        if (isset($this->delay)) {
            return $this->later($this->delay, $queue);
        }

        $connection = property_exists($this, 'connection') ? $this->connection : null;

        $queueName = property_exists($this, 'queue') ? $this->queue : null;

        return $queue->connection($connection)->pushOn(
            $queueName ?: null, new SendQueuedMailable($this)
        );
    }