Sometimes uninstalling a Microsoft Exchange server with the Control Panel's Add/Remove Programs applet isn't possible. The reasons vary, with one of them being that the Exchange server isn't able to communicate properly with the DCs. If you understand what occurs during an Exchange installation, you can manually undo the changes made by the Exchange setup process to remove an unwanted Exchange server.

Here are the changes that occur when you install Exchange server:

  1. The Active Directory (AD) schema is extended. New class and attribute definitions are created.
  2. The configuration information in AD is modified. Under the Configuration partition in the Services section, a new container named Microsoft Exchange is created. This container represents the Exchange organizational hierarchy.
  3. New user groups are created in AD. For example, in Exchange Server 2003 and Exchange 2000 Server, two user groups—Exchange Domain Servers and Exchange Enterprise Servers—are created in the domain's Users container. The Exchange servers in a domain are members of the Exchange Domain Servers group. The Exchange Domain Servers group is a member of the Exchange Enterprise Servers group. In Exchange Server 2010 and Exchange Server 2007, several new groups are created under a new organizational unit named Microsoft Exchange Security Groups, which resides in the root domain of the forest.
  4. The server's registry is changed. The changes occur in two registry keys: HKLM\Software and HKLM\System\CurrentControlSet\Services.
  5. A folder hierarchy for the Exchange installation files is created under a folder specified during the installation.

 If you want to manually uninstall an Exchange server, you must manually undo some of these changes:

  1. You don't need to worry about the AD schema changes that the Exchange installation made. These changes can't be reversed because you can't delete schema objects and attributes. Even if you could, it wouldn't be a good idea. If you have multiple Exchange servers, the remaining servers need these schema objects and attributes. Plus, if you uninstall your lone Exchange server, the schema objects and attributes that remain won't cause any problems. In fact, if you should later decide to install Exchange again, it would take a shorter time because the schema have been already changed.
  2. The server's configuration information in AD can be removed using the ADSI Edit console (ADSIEdit.msc). In Windows Server 2003 and Windows 2000 Server, this tool is one of the Support Tools, which aren't install by default. In Windows 2008, the ADSI Edit console is installed by default. To remove the configuration information, open the ADSI Edit console, and navigate to Services\Microsoft Exchange\ExchangeOrganizationName\AdministrativeGroups\RelatedOrganizationGroup\Serverswhere ExchangeOrganizationName is the name of your Exchange organization. After you locate the server you want to uninstall, simply delete it.

    Alternatively, you can delete the Microsoft Exchange container altogether. By doing this, you delete the Exchange organization's information in AD. However, be aware that removing a server this way isn't supported by Microsoft unless you're instructed to do so by its Customer Service and Support (CSS) staff. In addition, you run the risk of leaving semi-deleted objects or partially mail-enabled objects in AD. This isn't important if you don't plan to install Exchange into a forest again, but it is important if you do, as you can run into problems. To mitigate these risks, I delete the Microsoft Exchange container after moving the mail-enabled objects to other servers or after deleting them.
  3. You can delete the user groups related to the Exchange server, but this step isn't necessary. You should do this only if you want to undo all the changes.
  4. You need to delete the following registry keys on the Exchange server:
    • In Exchange 2010 and Exchange 2007, delete the HKLM\Software\Exchange and HKLM\Software\Exchange Server keys.
    • In Exchange 2003 and Exchange 2000, delete the HKLM\Software\Exchange key.
    In the HKLM\System\CurrentControlSet\Services key, delete the keys that were created for the Exchange Server services. In Exchange 2010 and Exchange 2007, all the keys related to the Exchange Server services start with MSExchange (e.g., MSExchangeIS). In Exchange 2003 and Exchange 2000, most of the keys also start with MSExchange. However, three keys have names that don't include this string. They are IMAP4Svc, POP3Svc, and RESvc.
  5. You should delete the files under the root Exchange Server folder.

By following these steps, you can manually uninstall an Exchange server. I've done so successfully several times.