Microsoft Exchange 2003 – Compatibility with Active Directory

Introduction to Exchange 2003’s compatibility with Windows 200x.

Understand the rules before you play the game!  A simple cross-check of your version of Exchange with your version of Windows, could save you hours of re-installing.  Most compatibility problems arise where you have Exchange 2000 with Windows Server 2003.

Topics for Compatibility


Compatibility between Exchange and Windows

Compatibility is the watchword when upgrading to Exchange 2003.  Pay careful attention to the version of Exchange and the version of Active Directory. In a perfect world you would move from Exchange 2000 running in a Windows 2000 domain to Exchange 2003 running in Windows 2003 domain.  Unfortunately, in the real world migration is not that straightforward.  What catches people unaware is this, not all combinations of Exchange and Windows operating systems are compatible.

Windows 2003


W2K Member in Windows 2003 DomainW2K in W2K DomainNT 4.0
Exchange 2003 Exchange 2003 Compatibility Exchange 2003 Compatibility Exchange 2003 Compatibility Exchange 2003 Compatibility
Exchange 2000 ??? Exchange 2003 Compatibility Exchange 2003 Compatibility Exchange 2003 Compatibility
Exchange 5.5 ? Exchange 2003 Compatibility Exchange 2003 Compatibility Exchange 2003 Compatibility


??? The situation is that you can have an Exchange 2000 on a Windows 2000 member server in a Windows Server 2003 domain.  But you cannot have Exchange 2000 on any sort of Windows Server 2003 machine.

? The situation with Exchange 5.5 in a Windows Server 2003 domain is that it must be on a Windows 2000 member server.

Note: As an indication of the complexity, this is my third version of the above compatibility table.  If you find any errors do let me know.

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Backwards Compatibility

Microsoft usually pride themselves on backwards compatibility, for instance, Windows Server 2003, Windows 2000 and NT 4.0 can all operate in the same domain.  So what is different with Exchange?  The answer lies in the schema, and the heart of the problem is that Exchange 2000 is incompatible with the new schema of Windows Server 2003.

The first problem then lies with Exchange 2000 and the ‘work around’ is to install it on a Windows 2000 member server as part of the Windows Server 2003 domain.

The second problem is that while Exchange 5.5 servers can operate in Windows 2000 domains, Windows Server 2003 domains do not support Exchange 5.5..   Some people say that this lack of backwards compatibility is laziness, others say that it means more security coupled with a desire to move forward without the tail wagging the dog.

Exchange 2003 is well behaved and integrates with Windows 2000 domains.


Where possible I like to keep systems in synch, so I recommend either:

1) Windows Server 2008, Exchange 2007 and Outlook 2007

2) Windows Server 2003, Exchange 2003 and Outlook 2003

3) Windows 2000, Exchange 2000, Outlook 2000.

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There are also two bonus tools in the free download, and all 3 have been approved by Microsoft:

  1. Bulk-import new users and mailboxes into Active Directory.
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90% of migrations will have no problems with compatibility.  A quick look at compatibility will save hours of frustration if you are in the 10% minority.  Systems with the same version number will work perfectly (Exchange 2000, with Windows 2000, 2003 with 2003).  The biggest challenge is to get Exchange 2000 to work with in a Server 2003 domain. 

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