I have the same issue. Problem occurs when there is a timeout on the resolving the DNS and dns_get_record returns false. Quick solution is to change line 183 class.validator.php to :
// According to RFC2821, the domain (A record) can be treated as an
// MX if no MX records exist for the domain. Also, include a
// full-stop trailing char so that the default domain of the server
// is not added automatically
if ($verify and !dns_get_record($m->host.'.', DNS_MX)) {
$r = dns_get_record($m->host.'.', DNS_A|DNS_AAAA);
if ($r===false) {
return false;
}
return 0 < @count($r);
}
