Microsoft Mail 3.5 does not necessarily require you to purchase Windows NT Server Client Access Licenses. It only requires them if the Mail Post Office is located on Windows NT Server.
To better understand how that affects your purchasing and deployment decisions, consider the following information. Microsoft Mail is network operating system (NOS)-independent. The Mail Post Office of shared file system mail, by definition, uses the underlying file-sharing services of the network upon which it runs. Microsoft Mail 3.5 has added a Windows NT-based multitasking message transfer agent (MMTA). The Mail Post Office and the MMTA can run on different servers with different NOSs.
If Windows NT Server is already providing licensed basic network file and print sharing services, then there is no additional Client Access License burden with running the Mail Post Office on that server. If Windows NT Server is not already providing those services, the Mail Post Office should be run on the network server (such as a NetWare server) that is providing the basic file and print services. The MMTA, though, would still run on Windows NT Server.
Microsoft Mail Server 3.5, like other server products, does require customers to have a Mail Server License to install the Post Office. If the Mail Post Office is running on Windows NT Server and that server does not already provide licensed basic network file and print sharing services, you also need to purchase a Windows NT Server Client Access License for each user accessing Microsoft Mail.
In addition to the Client Access Licenses for file and print sharing, you must also purchase client licenses for Microsoft Mail Server 3.5. These client licenses, though, are packaged differently from those of other server products, as follows: