Better validation of new users email address when creating account

Working with the user.module of 4.5.2 distribution I amended the user_validate_mail() function to provide additional checking for a new user.

This was inspired by the constant bounced emails I was getting each day from new users mistyping their email address.

Sorry that the code is not in patch form. The following code should be placed in user.module :-

function _user_check_dnsrr($maildomain, $rectype = 'MX')
{
  if(!empty($maildomain)) {
    if(function_exists('checkdnsrr')) {
      return checkdnsrr($maildomain, $rectype);
    } else {
      exec("nslookup -type=$rectype $maildomain", $result);
      foreach ($result as $line) {
        if(eregi("^$maildomain",$line)) {
          return true;
        }
      }

      return false;
    }
  }

  return false;
}

function user_validate_mail($mail) {
  if (!$mail) return t('You must enter an e-mail address.');

  list($username, $maildomain) = split("@", $mail);

  if (!valid_email_address($mail) || !_user_check_dnsrr($maildomain, "MX")) {
    return t('The e-mail address %mail is not valid.', array('%mail' => "<em>$mail</em>"));
  }
}

I have been using the above on http://www.bargainspy.co.uk/user/register without problem for a day now. Another step in the direction of helping users hide their general stupidity!