DNS query responses do not travel through a firewall in Windows Server 2003

Some mailservers behind firewalls ( like mine ) which do not allow transfer of UDP packets larger than 512 bytes may not be able to return the MX record for some ISP like earthlink.net. I came across KB article.

Windows 2003 server has included Extension Mechanisms for DNS (EDNS0) to allow larger packets. If you run this command on a 2003 server: "dnscmd Server Name/Config /EnableEDnsProbes 0", it fixes it without making any changes to the firewall.

Domains with this issue include AOL.com, Qwest.net, and EarthLink.net.