Non-flat roads do exist.

How does that even relate?

Mail encryption has nothing to do with how the mail is formatted (html vs plain text). And the client protocol for fetching the mail from the server also has nothing to do with that.

Well, who said the c in c/something is NOT commune? ;-)

Studded tires do exist.

Let me introduce you to https://davmail.sourceforge.net/

Yes it works pretty fine with stupid O365. You can basically use whatever mailclient you desire with it.

But what about those stupid apps that refuse to use the sd card?

It’s silly :-(