In the past I have written about the myths and pains around sending "secure" emails.
The bottom line is "forget it".
Secure email requires too much overhead and too much co-operation to ever work.
However, if you think about Messaging instead of emailing, then there is hope...a solution that seems good and easy for most people.
I've advocated simply avoiding attempting risky things (read communications) over the internet unless you are a bit of a techie.
The main reason being that with increasing numbers of steps, organizations and people between you and the destination for your secure communication, you can bet that sooner or later something will break and things will get leaked into the public domain.
So I am not surprised that it has taken me a while to stumble onto Signal.
Signal is a free, secure, point-to-point communication tool.
That means between you and the person you are communicating with, the whole path is encrypted. The things you say, type and send can only ever be seen / opened / read by the person you send them to.
You can do interactive messaging, voice and video calls and even send files. Plus a lot more besides AND to all of your friends regardless of computer/device religion/cult membership.
Of course, the caveat being that once they have them they can still "do things" with them, but at least you understand the trust level of that person and don't have to worry about the communication being intercepted.
Signal is the choice of journalists, whistle-blowers, IT experts, politicians and just about anyone else you can think of who needs to keep secrets in their line of work.
It isn't all scary stuff though. Filmmakers who want to keep their movies secret use it, medical professionals who need to transmit your private information securely can use it and so on.
Of course, if you need secure communications you shouldn't just take my word for it.
Then maybe test it a little and see how you like it. It is totally free and has no ads!!!
It may just be what you need to stop sending snail mail and turn off that bloody fax machine forever!!!
Have fun, David