A while ago I was asked to summarize why migrating to Exchange 2007 is different. So here is what I came up with, targeted at a CxO type.
Similar to the migration from Exchange 5.5 to Exchange 2000 the migration to Exchange 2007 is a paradigm shift in many ways. Exchange 2007 is both a rewrite of some Exchange 2003 code and new code for the many new features and changes. Most of Exchange 2007 was written using .NET and then compiled for Windows x64 for the first time, both of which required significant code changes. In addition, some APIs and other features were dropped from Exchange 2007 and other APIs and features were “deemphasized.” All of these changes may cause issues with any applications that currently interface with Exchange 2003. This possible impact to applications should be the biggest area of concern for organizations that have multiple in house or 3rd party developed applications.
Exchange 2007 also differs completely from previous version of Exchange on how messages are routed, clustering and high availability options, scalability, disaster recovery, resource scheduling, and general server placement due to the new server roles in Exchange 2007. Besides the changes to existing functionality, E2k7 includes many new features like unified messaging, Exchange Management Shell (command line), calendar concierge service, transport rules, managed folders, and others. Microsoft has also improved upon OWA, mobile device access and management, database architecture, management tools, and others. Finally, some features have been dropped from E2k7 like support for other mail systems (Exchange 5.5 and GroupWise), protocols (x.400, NNTP, NetBIOS, Named pikes, SPX, etc), and development interfaces (ExIFS, CDOEXM, Exchange web forms, Exchange SDK workflow, WMI, etc).
So migrating to Exchange 2007 should not be taken lightly and should include extensive testing and planning. All existing documentation and processes for installing, troubleshooting, monitoring, and daily operational procedures will need to be rewritten.
For more information see:
Or any of the articles\links here