Outlook Anywhere User Emailbox can't be resolved

Exchange 2007 has rebranded rpc/https which is now called Outlook Anywhere. It is quite easy to set up in EMS. Followed the standard set up steps, the outlook anywhere was successfully configured and working fine. However, it suddenly stopped working. All the setup are the same as before, the username and password are valid. It was not same as the problem other people dacing, the password window prompts constantly. The only problem is User Emailbox can't be resolved in Exchange server.

Following these a few steps to test the system:
1. Check “ValidPorts” under HKEY_LOCAL_MACHINE\Software\Microsoft\Rpc\RpcProxy, these are 6001, 6002, 6004 ports listed with the correct internal server name of exchange same as the exchange server name when configuring outlook anywhere;
2. Use RPCping, connected to Exchange server succesfully from external;
3. Use internet explore with URL https://FQDN/rpc/rpcproxy.dll successfully.

Contact Microsoft, they tested system using above approaches. But also can't identify the problem. After a few days, they found the IPv6 was enabled in Exchange server. Checked tcp/ip configuration, the IPv6 is disabled, but the IP address still has Ipv6 IP address, following the steps:

1. Uninstall IPV6 from window 2003 : Run this on command : netsh interface ipv6 uninstall
2. Add this in host file: system32\drivers\etc\hosts file:
IPv4 address hostname of the computer
IPv4 address FQDN of the computer

3. Reboot your server machine

Working Perfictly!!!