Microsoft Mail (or MSMail) 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. All were eventually replaced by the Exchange and Outlook product lines.
Versions 3.0 through 3.5 included email clients for MS-DOS, OS/2 1.31, Mac OS, Windows (both 16 and 32-bit), a separate Windows for Workgroups Mail PC WFW: Differences Between Win for Workgroups Mail & PC Mail. Support.microsoft.com (2006-10-30). Retrieved on 2013-07-17. client, and a DOS-based Remote Client for use over pre-PPP/pre-SLIP dialup modem connections. A stripped-down version of the PC-based server, Microsoft Mail for PC Networks, was included in Windows 95 and Windows NT 4.0. The last version based on this architecture was 3.5; afterwards, it was replaced by Microsoft Exchange Server, which started with version 4.0.
The client software was also named Microsoft Mail, and was included in some older versions of Microsoft Office such as version 4.x. The original "Inbox" (Exchange client or Windows Messaging) of Windows 95 also had the capability to connect to an MS Mail server.
Microsoft Mail Server was eventually replaced by Microsoft Exchange; Microsoft Mail Client, Microsoft Exchange Client, and Schedule+ were eventually replaced by Outlook (Windows and Mac).
Mail that needed to travel between postoffices were moved by an external MTA called External (external.exe), which originally ran on MS-DOS. A version of External for OS/2 1.31 was added with Microsoft Mail for PC Networks version 3.2, and a multitasking MTA for Windows NT was added with version 3.5. This ran in the OS/2 subsystem of Windows NT and Windows 2000, and consisted mostly of the Version 3.2a External with wrappers containing hooks allowing control by NT administration utilities.
The database design and passive nature of the server both created several weakness. A complete lack of distinction between "header" and "envelope" addressing data meant that now-standard functionality such as could not be implemented. Mailing lists were similarly problematic. Also, a single postoffice was limited to 500 mailboxes; a large enterprise would require many postoffices and many MTAs to connect these postoffices. 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. While the inbox could be synchronised, other folders could not be, meaning that only inbox messages could be accessed across the two client architectures. Plans to create a Mac OS client which could access .MMF storage were abandoned before version 3.0 shipped, though working - if buggy - versions did exist.
The Windows and OS/2 clients were built around an early version of MAPI called MAPI 0, and could in theory enable the client to talk to any server by replacing the MAPI DLL with a fully compliant DLL for the appropriate system. 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. The first and almost immediately recalled version of the Microsoft Press book on using Microsoft Mail accidentally used screenshots from the Xenix backend, revealing this concealed capability of the client.
Connection to UUCP-based email systems were supported indirectly, using the Microsoft Mail Gateway to SMTP client combined with a Unix system, typically running sendmail as a Smart host. SCO Unix and Interactive Unix were both recommended products for this structure, though any SMTP-UUCP smarthost-capable system would work.