How Outlook 2000 accesses Active Directory

This article describes how to disable directory service referrals on an Exchange 2000 computer.

Outlook 2000 uses a different method of Address Book access than Microsoft Outlook 97 and Microsoft Outlook 98. Initially, Outlook attempts to locate the directory service on the home Exchange Server computer. Because Outlook can only determine which version of Microsoft Exchange Server or Exchange 2000 that the system is running after Outlook installs Emsmdb32.dll (which runs after the Address Book provider Emsabp32.dll), Outlook uses the DSProxy process for the first session. After the client computer has contacted the DSProxy service (the client computer attempts all available transport protocols), a special referral is transferred back to the client computer, which indicates to the client computer to send all future directory requests to the global catalog server. Outlook retains this referral in the MAPI profile under the following registry key: The referral mechanism reduces the load on the Exchange 2000 computer and the latency for Address Book lookups; however, when you type an explicit server name into the profile, you must restart Outlook if that particular Active Directory server stops responding. In this scenario, the Exchange 2000 computer transfers Outlook a new referral to use. You may also receive the following error message from your Outlook client when the Active directory server that is persisted in the registry is unavailable In some scenarios, you may want to require Outlook clients (even the latest versions) to use the DSProxy process without being referred. The best example of such a scenario is when a firewall exists between the client computers and Active Directory servers. You can open the firewall to enable the Exchange 2000 computer to access Active Directory.

You can require Outlook clients to use the DSProxy process without being referred by indicating to the Exchange 2000 computer that it must not grant referrals. To implement this change, edit the registry:

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

1. Start Registry Editor.
2. Locate and click the following key in the registry:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeSA\Parameters
3. On the Edit menu, click Add Value, and then add the following registry value:
   Value name: No RFR Service
   Data type: DWORD
   Value data: 0x1
4. Quit Registry Editor.
5. For this change to take effect, you must restart the server or, at a minimum, restart Exchange System Attendant.

For additional information about how other MAPI clients access the Active Directory, click the article number below to view the article in the Microsoft Knowledge Base: