public static function queue($address, $subject, $content, $userId = null)
    {
        try {
            $email = new static;
            $email->user_id = $userId;
            $email->email = $address;
            $email->subject = $subject;
            $email->content = $content;
            $email->status = self::STATUS_PENDING;
            $email->attempt = 0;
            return $email->save();
        } catch (Exception $e) {
            Log::error($e->getMessage(), null, __METHOD__);
        }
        return false;
    }