How to force Outlook to connect to a specific global catalog server or to the closest global catalog server in its site

When you install Exchange Server in a child domain, the Outlook clients may try to communicate with the global catalog in the parent domain, this will cause a problem if the parent and the child domain is not in the same site or there is a firewall between the clients and the servers in the parent domain and cause the outlook to respond slowly.

To solve this issue you can force Outlook to communicate directly with the global catalog server in its site or with the closest catalog if the client moves between sites.
Notice that you need to edit a registry value, so make sure you take a backup of your registry before changing any value.

To force Outlook to communicate with the closest global catalog server:
-Open the Registry Editor. Click Start, click Run, type regedit.exe, and then click OK.
-Locate the following key in the registry:
HKEY_CURRENT_USER\Software\Microsoft\Exchange\Exchange Provider
You may have to create the registry path if it does not exist.
-On the Edit menu, click Add Value, and then add the following registry value:
Value name: Closest GC
Data type: REG_DWORD
Value data: 1
-Quit Registry Editor.

Or use the following command to create the key and the value:
REG ADD “HKEY_CURRENT_USER\Software\Microsoft\Exchange\Exchange Provider” /v “Closest GC” /t REG_DWORD /d 1

To force Outlook to communicate with the a specific global catalog server:
-Open the Registry Editor. Click Start, click Run, type regedit.exe, and then click OK.
-Locate the following key in the registry:
HKEY_CURRENT_USER\Software\Microsoft\Exchange\Exchange Provider
You may have to create the registry path if it does not exist.
-On the Edit menu, click Add Value, and then add the following registry value:
Value name: DS Server
Data type: REG_SZ (string)
Value data: FQDN.OF.GlobalCatalog
-Quit Registry Editor.

Or use the following command to create the key and the value:
REG ADD “HKEY_CURRENT_USER\Software\Microsoft\Exchange\Exchange Provider” /v “DS Server” /t REG_SZ /d GC.Child.Domain.Local