public function smtp(array $params)
    {
        //validate the user params
        if (!array_key_exists('username', $params)) {
            throw new Exception('We need a username');
        }

        if (!array_key_exists('password', $params)) {
            throw new Exception('We need a password');
        }

        $this->smtp = $params;
        $this->auth = true;

        return $this;
    }