protected function authXOAuth2()
    {
        $authStr = sprintf("user=%s%sauth=Bearer %s%s%s",
            $this->message->getFromEmail(),
            chr(1),
            $this->oauthToken,
            chr(1),
            chr(1)
        );
        $authStr = base64_encode($authStr);
        $in = "AUTH XOAUTH2 $authStr" . $this->CRLF;
        $code = $this->pushStack($in);
        if ($code !== '235'){
            throw new CodeException('235', $code, array_pop($this->resultStack));
        }
        return $this;
    }