I know you need to follow special procedures for removing the last server from a site or administrative group. Do I have to do anything special to remove the last Exchange Server 5.5 machine from a mixed-mode organization?

Yes, you do. Overall, the process is very similar to the steps outlined in the Microsoft articles "XADM: How to Remove the First Exchange Server in a Site" (http://support.microsoft.com/default.aspx?scid=kb;en-us;q152959)—for Exchange 5.5—and "XADM: Removing the First Exchange 2000 Server from the Site" (http://support.microsoft.com/default.aspx?scid=kb;en-us;q252486). The basics are the same: Rehome any public folders on the target server, migrate the Schedule+ Free/Busy folder, relocate or replace any connectors, and so forth. However, the sticking point is that Exchange System Manager (ESM) won't let you remove the last Exchange 5.5 server because it knows that the Site Replication Service (SRS) is tied to that server's presence. The solution is to not use ESM; instead, use the Exchange 5.5 Microsoft Exchange Administrator tool:

  1. Run Exchange Administrator and tell it to connect to whichever server is running the Exchange 2000 SRS.
  2. Select the Exchange 5.5 server and press Delete. Confirm that you want to remove the server, and—presto!—it disappears.
  3. Use the Microsoft Management Console (MMC) Active Directory Connector Management snap-in to force the Configuration Connection Agreement (ConfigCA) to replicate the server's deletion. (Right-click the ConfigCA for the SRS server you're connected to, and choose Replicate Now.)
  4. Wait for the deletion to replicate. Verify that the server is gone by launching ESM and making sure that you can no longer see the Exchange 5.5 server.
  5. Remove the SRS by expanding the Tools node in ESM, right-clicking Site Replication Service, and clicking Delete.

For more information, see Daragh Morrisey, "How to Remove the Last Exchange 5.5 Server," March 2002, InstantDoc ID 23769.