If you want to see which domain controllers/global catalogs your Exchange Server 2007 (RTM or Sp1) uses to query your Active Directory Forest, you can use the Exchange Management Shell cmdlet Get-ExchangeServer including the parameter Status. If you omit the parameter Status, you will notice that you won’t see which domain controllers and global catalogs are used by your Exchange Server.
[PS] C:\>Get-ExchangeServer | fl name,current*
Name CurrentDomainControllers
CurrentGlobalCatalogs : {}
CurrentConfigDomainController :
[PS] C:\>Get-ExchangeServer -Status | fl name,current*
Name: DCCurrentDomainControllers : {DC.nwtraders.com}
CurrentGlobalCatalogs: {DC.nwtraders.com}
CurrentConfigDomainController: DC.nwtraders.com