Windows 95 includes a Microsoft Mail Postoffice, workgroup edition. This means that everything is included that you need to set up and manage a complete e-mail system for your workgroup. A postoffice is simply a shared directory where e-mail is stored — users connect to the postoffice in order to send or retrieve mail.
Typically, one of the users in your workgroup is designated as the Mail Administrator. They create the postoffice on their machine by using the "Microsoft Mail Postoffice" applet in the Windows 95 Control Panel. A wizard is used to step the administrator through the process of creating the postoffice. The administrator can then use this wizard to add new users, delete users, or manage shared folders. The administrator shares the Postoffice directory, and the users enter the shared directory name the first time they start their Microsoft Exchange.
The Microsoft Mail Postoffice included in Windows 95 is a workgroup edition, meaning it is limited to exchanging mail with users on a single postoffice. A single postoffice can potentially support dozens of users, depending on the server performance of the postoffice machine. At some point, however, you may need to split people into separate workgroups, each accessing their own postoffice. At this point you will need to upgrade to a full Microsoft Mail Server. The full edition of Microsoft Mail Server allows mail to be routed between multiple postoffices, as well as to other e-mail gateways.
You can also easily upgrade your postoffice to a Microsoft Exchange Server, a client-server messaging system that provides not only e-mail services, but also personal/group scheduling, information-sharing applications ("groupware"), and forms and application design tools.