Do we need to upgrade our domain to Windows Server 2003 to migrate to Exchange Server 2003? We currently have two Windows 2000 domain controllers (DCs) and an Exchange 2000 Server system. We'll be migrating to a new Exchange 2003 server soon and wonder whether it would make sense to introduce a new Windows 2003 DC, run a mix of Windows 2003 and Win2K DCs, then gradually demote the Win2K DCs over the course of a year.
Well, you don't have to upgrade your domain; Exchange 2003 will run perfectly well in a Win2K Active Directory (AD) environment, although you'll need to run the Exchange 2003 version of ForestPrep to update the schema. However, several Exchange 2003 features, including support for Microsoft Volume Shadow Copy Service (VSS), are available only when you run Exchange 2003 on Windows 2003. The biggest feature you'll miss out on by not upgrading your domain is Remote Procedure Call (RPC) over HTTP, which requires that all Global Catalog (GC) servers used by Exchange or Outlook run on Windows 2003. Many performance, stability, and security improvements in Windows 2003 are also compelling enough to make the upgrade worthwhile. Gradually demoting your Win2K machines will give you a fairly graceful migration path, and you might find that you can accelerate your timetable if the migration goes smoothly.