PHP - Check MX Records Against IP Bans

check_mx.php

<?php

$domain = 'spamdomain.com';

function banMxServer($domain)  {
    $banlist = [
        '1.2.3.4',
        '2.3.4.5',
    ];

    if (!getmxrr($domain, $mxs) || empty($mxs)) {
        return false;
    }

    foreach ($mxs as $mx) {
        $ips = gethostbynamel($mx);

        foreach ($ips as $ip) {
            if (in_array($ip, $banlist)) {
                return true;
            }
        }
    }  

    return false;
}