[canucker2016]

Yes, MS Mail for PC Networks used a shared file system for email.

The Workgroup Apps (WGA) divison ran MS Mail for PC Networks since they produced MS Mail. Gotta dogfood your product. The WGA email system used a Xenix gateway to connect with the rest of Microsoft.

The rest of Microsoft ran MS Mail for Windows with a Xenix email backend and address book, since MS was already using Xenix before MS Mail for PC Networks existed.

Windows for Workgroups 3.11 contained a one postoffice-version of MSMail, (which could be upgraded to the full version).

Some more Microsoft email-related history at https://en.wikipedia.org/wiki/History_of_Microsoft_Exchange_...