Answer: If you need to configure Exchange Server to use a different DNS server for internal or external DNS resolution than the one on the Server’s network card you can do this by following the steps below.
To configure Exchange Server 2010 to use a different DNS server use the following steps:
Open EMC -> Server Configuration -> Hub Transport -> Double click on the Hub server.
In the Hub server properties click on the Internal DNS lookups tab or the External DNS lookups tab.
If you need to change the DNS server just tick the Use these DNS servers box and type the new DNS server IP address.