It literally is, Outlook for Windows uses the IE9 engine to render HTML email, IIRC. And even then not everything is supported.

Which is an improvement over when it used to use the Word engine to render HTML email, IIRC.

You aren't trying to send an angular SPA in an email, are you?

Actually, it uses the Word engine for HTML rendering.

Kind of. Though if outlook magically goes away we'll still make emails with <table> because most clients still do not support even flex-direction. Outlook is just exceptionally bad with stuff like width:100px working on table elements, but not on <div>, or padding working only on specific elements.