While it is possible to physically upgrade-in-place from NT 4.0 to Windows Server 2003, it is usually not recommended due to older hardware, better security and upgrade failure concerns. It is not possible to do an upgrade-in-place of Exchange 5.5 to Exchange 2003. For all but the smallest organizations, a better approach is to migrate in the following way: introduce a new Windows 2003 Active Directory server, migrate the accounts from NT 4.0 using Active Directory Migration Tool (ADMT), synchronize the Exchange 5.5 Directory with Active Directory using Active Directory Connector (ADC), introduce a new Exchange 2003 server, and then migrate the mailboxes, public folders and connectors. The basic approach is the same for a small, medium or large organization such as a university. See chapter 4 of the Exchange Server 2003 Deployment Guide.
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