better dns verification

Hello,

Can you update the dns check to search for an mx record replacing :

return $response = (checkdnsrr($domain[1]) ? true : false);

with

return $response = (checkdnsrr($domain[1], "MX") ? true : false);

For exemple : [email protected] is accepted as gmail.fr domain exists, but it should not be accepted as valid because gmail.fr has no MX record.

Domains without MX records have no mail server, so they should not be validated by this plugin.

Thank you.