A. When Outlook 2000 and later clients query Exchange for address book content, the Exchange DSProxy service initially passes back address book information that's based on GC information for the first query. For subsequent address book queries, Exchange refers the clients to a GC so that DSProxy doesn't need to perform additional tasks. If you don't want to let Outlook clients communicate directly with a GC and prefer that they communicate with the Exchange server, which is likely the case if you're using Microsoft ISA Server to publish remote procedure calls (RPCs) to Internet-based Outlook clients that aren't using RPC-over-HTTP Secure (HTTPS), you can stop the Exchange server from referring clients by performing these steps:

  1. Log on to each Exchange server as an Administrator.
  2. Start the registry editor (regedit.exe).
  3. Navigate to the HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeSA\Parameters registry subkey.
  4. From the Edit menu, select New, DWORD value.
  5. Enter a name of "No RFR Service" and press Enter.
  6. Double-click the new value and set it to 1. Click OK.
  7. Restart the Exchange server (or at a minimum, the Exchange System Attendant).

It's important to note that enabling the No RFR Service setting will cause the Exchange server to authenticate the client, which means that during the Outlook client connection, the Outlook client doesn't need to communicate with Active Directory (AD). Normally the Exchange server would instruct the Outlook client to authenticate to a domain controller (DC).