public function Master_Preview($masterId, $contentType, $distributionList, $userId, $emails) {
        $ret = false;
        $contentTypes = array('HTML', 'PLAIN', 'BOTH', 'USERPREFERENCE');

        if (in_array($contentType, $contentTypes) === true) {
            if (is_string($distributionList) === true xor (is_int($userId) === true && is_array($emails) === true)) {
                $data = new \stdClass();
                $data->contentType = $contentType;

                if (is_string($distributionList) === true) {
                    $data->distributionList = $distributionList;
                } else {
                    $data->manualList = new \stdClass();
                    $data->manualList->userId = $userId;
                    $data->manualList->emails = $emails;
                }

                $ret = $this->_call_api('post', "{$this->_url}/masters/$masterId/sendPreviews?validate", $data);
            }
        }

        return $ret;
    }