I used to bang on about the emails-are-postcards thing that Andy Yen talks about here. But I gave up, because nobody seemed interested. Back when the email client Turnpike natively allowed PGP (Before Someone Stepped In And Stopped It) I was becoming used to using PGP-signed emails, and, when appropriate, encrypted ones too.
I signed up for a free protonmail account some time ago. If you believe in the concept of privacy, I urge you to do so, too. We need to make emails-in-envelopes commonplace, before Those Who Would Read Everything We’d Like To Keep Private In The Name Of Anti-Terrism* lock the door and throw away the keys.
* … all but Those Of You Who Have Nothing To Hide (in your dreams).