XADM: How to Install Exchange 4.0 in an Exchange 5.0 Site

This article concerns a scenario in which you have an existing Microsoft Exchange Server site and one of the servers in that Site is running Exchange Server 5.0. This article tells you how to install Exchange Server 4.0 in an Exchange Server site that contains an Exchange Server 5.0 computer or is in a site connected to another site that contains an Exchange Server 5.0 computer.

The Support folder on the Exchange Server 5.0 CD contains an updated Setup.exe file. Use this Setup.exe file when setting up Exchange Server 4.0 in a site that contains an Exchange Server 5.0 computer. To set up Exchange Server 4.0:

1.	Copy the Setup\<platform> (such as I386, Alpha, and so on) directory from the Exchange Server 4.0 CD to a blank directory on the hard disk drive.
2.	Copy Support\Exch40\<platform>\Setup.exe from the Exchange Server 5.0 CD to the directory that you created in step 1. This will overwrite the older Setup.exe file.
3.	From the directory you created in step 1, run the new Setup.exe program that you copied in step 2.

These steps must be followed because when Exchange Server 5.0 is installed in a Site with Exchange 4.0 Server computers, the schema of all the servers in that site and all sites that have a Directory Replication Connector to that site will be upgraded and the older version of Setup.exe will not work correctly.

Once this is done, installing Exchange Server 4.0 in that site will fail because the Exchange Server 4.0 directory handle these new object types. Replication with the other servers will fail, or the server will stop operating correctly.

The new version of Setup.exe supplied on the Exchange Server 5.0 CD was modified so that the Exchange Server 4.0 can handle these new object types, allowing Setup to work correctly.