Most of the discussion about Exchange Server 2003 (code-named Titanium) has concentrated on the release's new features and functionality, which is probably as it should be. However, changes to some familiar Exchange 2000 Server features warrant some notice.
The most visible change is to Exchange 2000's real-time collaboration services: the Chat service (which, by best estimates, only about 2 percent of Exchange 2000 and Exchange Server 5.5 sites have installed), the Instant Messaging (IM) service, and the Exchange 2000 Conferencing Server. Exchange 2003 replaces these services with the Windows real-time communications (RTC) platform, which is part of Windows Server 2003. You can continue to use the Exchange Conferencing Server and the Exchange IM service when you migrate to Exchange 2003--if you keep some Exchange 2000 servers around to run those services. However, the new RTC platform has some nifty features--including full support for the interoperable Internet Engineering Task Force (IETF) Session Initiation Protocol (SIP)--that will probably make you want to move to RTC. (Go to the URL below for more details about the forthcoming RTC feature set.)
The next significant change is the disappearance of the Exchange 2000 Key Management Service (KMS). You might not have heard of the KMS unless you take advantage of Exchange 2000's advanced security support for public-key encryption of email. The KMS ties Exchange's email-specific encryption and security functionality to Windows Certificate Services, which issues, revokes, and renews the digital certificates that Exchange clients use to secure email. The KMS's departure isn't a problem, though, because Windows 2003 Certificate Services has a great deal more functionality than the Windows 2000 version and fully supports Exchange advanced security.
Another change is that Exchange 2003 includes a new version of the Exchange System Manager (ESM). The new ESM lets you manage Exchange 2003, Exchange 2000, and Exchange 5.5 servers from a Win2K or Windows XP system. However, to manage Exchange 2000 components that don't exist in Exchange 2003 (e.g., the IM service, the KMS), you'll probably need to keep a copy of the Exchange 2000 ESM.
What about third-party components? Most vendors are working on Exchange 2003 support--for example, major backup vendors are adding support for the Microsoft Volume Shadow Copy Service (VSS), and antivirus vendors are retooling their products to support the revised Antivirus API (AVAPI) scanning interface. As we've seen with each Exchange release, though, some vendors do a better job of testing and supporting new versions than others do. When you prepare to migrate, contact your third-party vendors to find out whether they're supporting Exchange 2003, then vigorously test the updated products to ensure that those products work properly.