To migrate to a brand new forest, you will need some native tools or consider third-party tools. The migration will involve copying the user accounts and physically exporting and importing mail into the new environment.
To upgrade path from Exchange 2000 to Exchange 2003, you need to upgrade to Exchange 2003 before upgrading your infrastructure to Windows 2003. See: You cannot install Exchange 2000 on a computer that is running Windows Server 2003
Then you need to go through the steps required for the upgrade. You load your Exchange 2003 CD, and follow the ExDeploy steps as it walks you through the upgrade process.
- Ensure Service Pack 3 or later is applied. If not, the upgrade won't be possible.
- Verify you have NNTP, SMTP and WWW services installed and enabled. This should have been covered during your installation of Exchange 2000, but it's listed nonetheless.
- Remove the IM Server, Chat, Key Management Server, MS Mail and the Lotus ccMail connector prior to the upgrade. If you need these, you should consider keeping Exchange 2000 until the dependency is eliminated. (Public Service Announcement: Finish your MS Mail migration and any legacy migrations first!)
- Install the Windows 2000 support tools, located on the Windows 2000 server CD \support\tools\SETUP.EXE.
- Run DCDIAG to ensure proper network resolution and DNS resolution.
- Run NetDiag to ensure network connectivity.
- Run ForestPrep.
- Run DomainPrep for each child domain controller.
- Run Setup. The installation can take some time, so please don't cancel or reboot your server in the event you believe something is wrong. I would suggest you get some coffee and come back to it -- you will see it completed a pre-install and post-install process during the upgrade.
This is an abbreviated answer. You should also read the Microsoft tips on the OS upgrade process: Upgrade to Exchange Server 2003.
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This was first published in November 2005