public function is_valid() {
        $ret = false;

        if (is_null($this->name) === false && is_null($this->type) === false &&
            (is_null($this->subtype) === false || $this->type !== 'DISTRIBUTIONLIST') &&
            is_null($this->subscriberList) === false
        ) {
            $ret = true;
        }

        return $ret;
    }