Yeah, I know how that goes. Our formatting is pretty neutral — we just offer a good readable text size, make everyone use the same font and colours so no one is writing in hot pink 16pt Comic Sans, allow Markdown, have a mobile design and dark mode in the emails. I've personally spent the midnight hours to make sure this all works nicely with existing email.
It's an ongoing battle but not an intractable one. It's not perfect, but we've gotten it to pretty good already. It definitely survives being quoted and otherwise chomped on by Gmail, Mail.app, Outlook, iOS and Android mail clients, which are our five main test cases.
