Why Not Just Use ESM?
The ESM window in Figure 1 shows two Exchange servers: Tazmania (an Exchange 2003 server) and Mirage (an Exchange 2007 server). Because ESM can display both, you might wonder why you shouldn’t use ESM to manage both versions of Exchange. This seemingly simple question actually has a fairly complicated answer—I could probably write an entire article on the subject. I don’t have room to do that here, so I’ll keep the explanation short. With Exchange Server 2003, Microsoft had to introduce new features while making Exchange Server 2003 compatible with earlier versions of Exchange. Some of the new features simply couldn’t be made backward-compatible, though, so Microsoft adopted the concept of native mode. The basic idea was that Exchange 2003 could coexist with legacy Exchange versions, but if it did, not all its features could be used. After all legacy Exchange servers had been decommissioned or upgraded, the administrator could set Exchange 2003 to run in native mode and take advantage
