Edge Transport Server Fails DNS Query When Emailing to one Specific Domain

This issue occurs for the same domain across three different edge transport servers.

All servers are Windows 2008 STD SP2, Exchange 2007 SP1 U9.  Emails are delivered using DNS connector from edge.  Emails to this one specific domain would sit in the retry queue with DNS query error until NDR was generated.  Connectivity Logging generated the following:

2009-09-01T19:52:23.539Z,08CBEDE9198E2DC3,SMTP,subdomain.domain.com,>,DNS server returned ErrorRetry reported by 208.241.124.200
2009-09-01T19:52:23.539Z,08CBEDE9198E2DC3,SMTP,subdomain.domain.com,-,The DNS query for 'DnsConnectorDelivery':'subdomain.domain.com':'cd771f71-77a3-4aca-b002-86f477816910' failed with error: ErrorRetry

I changed the servers DNS settings to different servers with the same response.  Validated that manual MX lookups worked, and that I could telnet to any of the three MX records and deliver mail via telnet.

I did a packet capture and received the following:

12    32.280037    172.28.16.55    208.241.124.200    DNS    Standard query AAAA SMTPSERVER.subdomain.domain.com

So what is happening is the Edge servers are only performing IP6 lookups, and throughout the log, only for subdomain.domain.com do they NOT perform a regular IP4 A record lookup.  I then went about disabling TCP/IP6 as per this article:

http://technet.microsoft.com/en-us/network/cc987595.aspx

this stated to do the following:

Alternately, from the Windows XP or Windows Server 2003 desktop, click Start , point to Programs , point to Accessories , and then click Command Prompt . At the command prompt, type netsh interface ipv6 uninstall .

To remove the IPv6 protocol for Windows XP with no service packs installed, do the following:

1. Log on to the computer with a user account that has local administrator privileges.
2. From the Windows XP desktop, click Start , point to Programs , point to Accessories , and then click Command Prompt .
3. At the command prompt, type ipv6 uninstall .
   

Unlike Windows XP and Windows Server 2003, IPv6 in Windows Vista and Windows Server 2008 cannot be uninstalled. However, you can disable IPv6 in Windows Vista and Windows Server 2008 by doing one of the following:

• In the Network Connections folder, obtain properties on all of your connections and adapters and clear the check box next to the Internet Protocol version 6 (TCP/IPv6) component in the list under This connection uses the following items .
  
  This method disables IPv6 on your LAN interfaces and connections, but does not disable IPv6 on tunnel interfaces or the IPv6 loopback interface.
• Add the following registry value (DWORD type) set to 0xFF:
  
  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters\DisabledComponents
  
  This method disables IPv6 on all your LAN interfaces, connections, and tunnel interfaces but does not disable the IPv6 loopback interface. You must restart the computer for this registry value to take effect.

I did the above, and still, the Edge Transport servers would only perform AAAA lookups, and messages would sit in the queue.





As temporary workaround, created new send connector with the three available MX hosts as possible smarthosts for subdomain.domain.com, and this allowed email flow.

I've tried disabling the TCPIP6, and still doesnt work.  Any suggestions?