By default an Exchange 2007 Hub Transport server and Edge Transport server will use the DNS settings of any of its network adapters to perform DNS lookups of destinations both inside and outside the Exchange organization. You can use the Exchange Management Shell and the Exchange Management Console to set create a different custom list of DNS servers to be queried for destinations inside and outside the Exchange organization.
The following EMS output shows how the default settings are changed to let Exchange perform DNS lookups for destinations outside the Exchange organization against a DNS server with IP Address 192.168.1.1.
[PS] C:\>Get-TransportServer nts12 | fl *dns*
ExternalDNSAdapterEnabled : True
ExternalDNSAdapterGuid : 00000000-0000-0000-0000-000000000000
ExternalDNSProtocolOption : Any
ExternalDNSServers : {}
InternalDNSAdapterEnabled : True
InternalDNSAdapterGuid : 00000000-0000-0000-0000-000000000000
InternalDNSProtocolOption : Any
InternalDNSServers : {}
[PS] C:\>Get-TransportServer nts12 | Set-TransportServer -ExternalDNSAdapterEnab
led:$False -ExternalDNSServers 192.168.1.1
[PS] C:\>Get-TransportServer nts12 | fl *dns*
ExternalDNSAdapterEnabled : False
ExternalDNSAdapterGuid : 00000000-0000-0000-0000-000000000000
ExternalDNSProtocolOption : Any
ExternalDNSServers : {192.168.1.1}
InternalDNSAdapterEnabled : True
InternalDNSAdapterGuid : 00000000-0000-0000-0000-000000000000
InternalDNSProtocolOption : Any
InternalDNSServers : {}
This configuration can be done by using the Exchange Management Console, by going to Server Configuration, and selecting the properties of your Hub Transport server and change the required settings on the property pages External DNS Lookups and Internal DNS Lookups.