If you are going to deploy Exchange 2007, although some features will work by allowing the Exchange server to contact a remote domain controller via a VPN tunnel, it is strongly recommended that you have a local domain controller in the same subnet as the Exchange server. This domain controller doesn’t need to be a local DNS server – the critical thing it needs to be is a Global Catalog server.

How to create a new global catalog on the destination global catalog server

To create a new global catalog:

  1. On the domain controller where you want the new global catalog,
    start the Active Directory Sites and Services snap-in. To start the
    snap-in, click Start, point to Programs, point to Administrative Tools, and then click Active Directory Sites and Services.
  2. In the console tree, double-click Sites, and then double-click sitename.
  3. Double-click Servers, click your domain controller, right-click NTDS Settings, and then click Properties.
  4. On the General tab, click to select the Global catalog check box to assign the role of global catalog to this server.
  5. Restart the domain controller.

Allow sufficient time for the account and the schema information to
replicate to the new global catalog server before you remove the global
catalog from the original domain controller.