[watersb]

To me, the interesting bit here is that Outlook is still using the Microsoft Word layout engine.

That's what's going away: Outlook on Windows moves to the Chromium-lineage MS Edge web layout.

I idly wonder about legacy DIME (binary multipart MIME encoding from 20th Century Office products), but it's easier to run entire legacy systems inside a web render these days.

One of the Word layout engines really boosted Microsoft's dynamic web browser implementation in the early days; they had this compact, fast thing they could use already. IE 4.0 era.