--- ./common.inc.orig	2008-12-12 20:12:09.000000000 -0800
+++ ./common.inc	2008-12-12 20:23:58.000000000 -0800
@@ -923,7 +923,7 @@
   $ipv4 = '[0-9]{1,3}(\.[0-9]{1,3}){3}';
   $ipv6 = '[0-9a-fA-F]{1,4}(\:[0-9a-fA-F]{1,4}){7}';
 
-  return preg_match("/^$user@($domain|(\[($ipv4|$ipv6)\]))$/", $mail);
+  return (preg_match("/^$user@($domain|(\[($ipv4|$ipv6)\]))$/", $mail, $matches) && (!function_exists('checkdnsrr') || checkdnsrr($matches[1], "MX")));
 }
 
 /**