To upgrade the Standard Edition of Microsoft Exchange Server to the Enterprise Edition of Microsoft Exchange Server, run the Setup program from the Exchange Server Enterprise Edition CD and click the Reinstall button.
To install any additional components or connectors included in the Enterprise Edition of Exchange Server, run the setup program again and click Add/Remove.
Note: Any Exchange service packs or hotfixes must be reapplied after you upgrade. Once upgraded, you cannot downgrade Exchange Enterprise Server edition to the standard version of Exchange Server.
For more information about a case in which the upgrade is not possible because of the different packaging of the product, read the following Microsoft Knowledge Base article, XADM: No option to upgrade from Exchange 2000 Server Standard Edition to Exchange 2000 Enterprise Server.
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