The real trick to removing Exchange Server 2003 from your organization is reassigning the Recipient Update Service. Setup will not allow you to uninstall Exchange Server 2003 until the Recipient Update Service has been reassigned to another server. This is ironic since Exchange Server 2007 doesn't even use the Recipient Update Service. Even so, this task must be performed.
Reassigning the Recipient Update Service is fairly easy. Begin the process by opening the Exchange System Manager. Now, navigate through the console tree to Recipients | Recipient Update Service.
There are two listings for the Recipient Update Service. There is an enterprise listing, and a domain listing.
At this point in the process, you must right click on the enterprise listing for the Recipient Update Service, and then choose the Properties command from the resulting shortcut menu. When you do, the Exchange System Manager will display the Recipient Update Service properties sheet.
You will notice that the Recipient Update Service has been assigned to a specific Exchange server. By default, the server that is listed is an Exchange 2003 server. You must click the Browse button, and then choose an Exchange 2007 server from the list. After doing so, click OK to close the Recipient Update Service properties sheet.
Now it's time to turn our attention to the domain listing for the Recipient Update Service. We will do the exact same thing for this listing that we did for the enterprise listing. Right-click on the domain listing and choose the Properties command from the resulting shortcut menu to reveal the Recipient Update Services properties sheet. Now, click the Browse button next to the listing for the Exchange server, and choose an Exchange 2007 server from the list. Click OK to close the properties sheet, and were done.
Conclusion
Now that the Recipient Update Service has been reassigned you should have no trouble uninstalling Exchange server 2003. Simply run the Exchange Server 2003 Setup program, and then use the Change/Remove option to complete the uninstallation process.
This gets trickier if you are removing Exchange 2003 SP2 from an Exchange 2010 Environment. Exchange 2010 also no longer uses the RUS, but the option to move RUS to 2010 does not exist. If you follow Microsoft’s steps for removal of Exchange 2003, you may have already deleted both the Enterprise and Domain RUS using ADSI Edit. This will create error messages which prevent uninstallation of Exchange 2003 SP2. Leave both of the RUS instances (Enterpise and Domain) alone. When you try to uninstall you will be prompted to move the RUS. Since you cannot, you can fool Exchange 2003 into thinking they were moved.
If you already deleted the two RUS, restore them from an AD backup (that’s where they live, not on the Exchange server) and then edit the following location using ADSIedit.msc :
CN=Configuration,CN=<domain> > CN=Services > CN=Microsoft Exchange > CN=<Exchange organization name> > CN=Address Lists Container > CN=Recipient Update Services.
Double click on each RUS in the right hand pane and scroll down to the msExchAddressListServiceLink attribute. Click on edit and carefully change the value to the location of the new Exchange 2010 Server, This will not move the RUS, only change the location in the AD Schema, and fulfill the Exchange 2003 requirement for moving the RUS somewhere else.
Using Add/Remove programs, uninstall Exchange 2003 without issue. It works, I did this last week, and have yet to even remove the Exchange 2010 RUS attribute from ADSI.
Enjoy-
You can then verify the changes in Exchange 2003 System Manager, and once these changes are made using ADSI, easily use Add remove programs to cleanly, and easily remove Exchange 2003 from your organization.
I hope this is helpful, as it took some time to creatively come up with this solution.