@inthehands I know of those, and the security provided by them is only bolted on a system never meant to be secure. There are so many issues: conflating encryption with authentication, insecure by default, key management, no group recipient encryption support with changing members (e.g. mailing lists), additional devices are hard to authorize.
Looking at instant messengers, modern messengers like Signal or WhatsApp solved a lot of the issues of their predecessors. I'd like to know how mail would look if it were to be designed today with all we know.