Previously, Exchange came in two editions: standard and enterprise. The difference between the two editions stems from connectors and their licensing. (You must license connectors on servers.) The previous Enterprise Editions included not only a full range of connectors, but also their licensing at no additional cost. Thus, people with networks inevitably opted for the Enterprise Edition, and those with a standalone server chose the Standard Edition.

Choosing the appropriate edition becomes a little more complicated with the advent of the NT Server, Enterprise Edition (NTS/E). Microsoft is using Exchange 5.5 to draw a clear line between standard functionality and a set of high-end features that are of interest to servers that must support large user communities. These guidelines can help you decide which edition to use:

  • If you want to run a standalone Exchange server, use Exchange 5.5, Standard Edition and NT Server, Standard Edition.
  • If you want to run a network of Exchange servers but aren't interested in the high-end features, use Exchange 5.5, Standard Edition and NT Server, Standard Edition. If you use the X.400 connector to link Exchange sites, however, you'll have to use the Exchange 5.5, Enterprise Edition or purchase the X.400 connector separately.
  • If you want to run a network of Exchange servers incorporating massive servers, use the Exchange 5.5, Enterprise Edition and NTS/E.
  • If you want an information store larger than 16GB, use Exchange 5.5, Enterprise Edition and either version of NT Server.
  • If you want to cluster your network, you must use Exchange 5.5, Enterprise Edition and NTS/E.