When using deep MX check on @umcg.nl which resolves to 192.87.23.73 and 192.87.23.74 the _isReserved function returns false, though the address isn't local or reserved but valid.

Also the function _isReserved does only check the first ip since it uses the function gethostbyname. For instance the hostname mx1.hotmail.com returns 12 host records.

I've rewritten the function using a regex and gethostbynamel so all the ip's will be checked.

/**
 * Returns if the given host is reserved
 *
 * @param string $host
 * @return boolean
 */
private function _isReserved($host)
{
    if (preg_match('/^([0-9]{1,3}\.){3}[0-9]{1,3}$/', $host)) {
        $hostlist = array($host);
    } else {
        $hostlist = gethostbynamel($host);
    }
    if (empty($hostlist)) {
        return false;
    }
    foreach ($hostlist as $host) {
        if (!preg_match('/^(0|10|127|128\.0|169\.254|172\.(1[6-9]|2\d|3[01])|191\.255|192\.168|192\.0\.0|192\.0\.2|192\.88\.99|198\.18|198\.19|198\.51\.100|203\.0\.113|223\.255\.255|22[4-9]|2[345]\d)\./', $host)) {
            return false;
        }
    }
    return true;
}