Coexistence is a state in which various versions of Exchange are
installed and running in the same organization. When you run your
Exchange organization in mixed mode, coexistence is possible. Each
version of Exchange can detect the other and share data with
Implementing Exchange 2000 requires time and planning. Coexistence is a viable solution for organizations wanting to implement the functionality Exchange 2000 immediately, before migration is complete.
Exchange 2000 is the first release of Exchange that relies completely on the directory provided by the operating system. Earlier versions of Exchange were integrated with the Windows NT security model, but rich directory information was contained in a separate database (Dir.edb). Because of its new architecture, for Exchange 2000 to fully coexist with earlier versions of Exchange, replication between Active Directory and the legacy Exchange 5.5 directory must take place. Replication is coordinated by Active Directory Connector (ADC).
For more information about coexistence and upgrading, see Microsoft Exchange 2000 Server Planning and Installation.
This section includes the following topics:
Related TopicsManaging Active Directory Connector