Microsoft Mail (or MS Mail or MSM) was the name given to several early Microsoft e-mail products for local area networks, primarily two architectures: one for Macintosh networks, and one for PC architecture-based LANs.

It was based on Network Courier, a LAN email system produced by Consumers Software of Vancouver, B.C., which Microsoft had bought.

Clients used mapped network drives and file sharing to write mail to the postoffice.

A complete lack of distinction between "header" and "envelope" addressing data meant that now-standard functionality such as Bcc: could not be implemented.

Since scheduling data and address lists were also stored locally in these postoffices, moving schedule and global address book information required yet more, separate agents called Dispatch and Microsoft Schedule+ Distribution Agent.

Dispatch would synchronise the various copies of the Global Address List using MSMail 3.x Directory Synchronization Protocol.

Further, the differing storage mechanisms made using MSMail across multiple client architectures problematic at best.

Unlike the Microsoft Mail 3.x server product, the clients could support Bcc: functionality.

This functionality was not exposed to Microsoft Mail for PC Networks users due to limitations in the server architecture, but the corporate internal MAPI.DLL enabling these particular clients to talk to Xenix-based mail transport systems utilised this functionality.