regex (preg_match) tld question

greetings all- question : what would be a way to use preg_match to check all tlds ? what are the possible types of tlds to watch out for ? here is snippet, all thoughts apprecaited. is there a better way to go about doing this ? function ValidateField($field,$value) { if ($field == 'email_address' && $value) { if (!preg_match('/^[_\.\'0-9a-z-]+@(\w+\.)+( ALL TLDS )$/',$value)) { ^^^^^^^^ print "Email is invalid"; / $good = 0; check all tlds } $class->next_field(); continue; } } or should i just look up the host ? if a host is temp down will it still validate ? thank you. philip -- be outside the box.