Did Microsoft never run Microsoft Mail internally?
It was an email system that ran on top of file system. If I recall, mail clients connected over a networked drive to access mailboxes. So it was never regarded as being very scalable.
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).
It was an email system that ran on top of file system. If I recall, mail clients connected over a networked drive to access mailboxes. So it was never regarded as being very scalable.