That's ironically still the easiest way to go for HTML emails as the output is almost guaranteed to display well across various email clients that don't implement CSS properly (Outlook).
IIRC Outlook[1] just uses the Word engine internally, so it's going to share the same quirks.
(I also seem to remember that Internet Explorer's Trident engine started as a fork from Word, although that's presumably a bit less direct in the later versions).
[1] At least proper desktop Win32 Outlook, not the dozens of other things Microsoft have called Outlook.
