Corporate users who migrate to Exchange 2007 will face mandatory infrastructure changes that, while advancing security and management, could add complexity and costs to their networks.
Beyond the 64-bit-only platform, major changes include a new role-based architecture that could require users to roll out as many as five types of Exchange servers to support functions such as remote client access, transport and routing, mailboxes, and unified messaging. The current versions of Exchange give users two deployment options: front-end servers and back-end servers.
Users also will face new clustering limitations and will have to eliminate all Exchange 5.5 servers from their environments. In addition, they will not be able to do in-place upgrades between Exchange 2000-2003 and Exchange 2007. And Exchange no longer will have its own site topology, but will run on top of Active
