http://j4dhkkxfcg2wdksyueimyoykwhirscttska5wtag6hvhqoqfphqd7yad.onion/en/blog/first_half_of_2020
Some providers out there that provide some sort of end-to-end encryption, create a form of walled garden or closed ecosystem where you need to use only a mail client provided by the platform (no choice in clients), are incompatible with other providers (own in-house developed encryption), do not allow you to control the encryption keys (you don't really own the keys as you cannot easily extract them, generate them on a separate machines, back them up, all in the name of making it "easy"...