MagePal\GmailSmtpApp\Model\Transport::sendMessage PHP Method

    public function sendMessage()
    {
        try {
            parent::send($this->_message);
        } catch (\Exception $e) {
            throw new \Magento\Framework\Exception\MailException(new \Magento\Framework\Phrase($e->getMessage()), $e);
        }
    }