I am a firm believer that there are many privacy techniques you should focus on before encrypted messaging because they will offer you much more “bang for your buck,” things like good passwords, two-factor authentication, and even encrypted email. That said, I still believe that encrypted messaging is a critical part of a well-rounded privacy and security strategy. While the vast majority of our day-to-day conversations may be benign, it can still offer a lot of insight into who we are as people – our routines, likes, and personal thoughts. This information – mundane or not – is worth protecting.
Besides being a form of messaging (so the text somewhat contradicts itself), typical email is a deeply insecure protocol.
In my opinion, it's probably impossible to secure without making a new protocol or making such drastic changes that it might as well be considered one.
Here are some key concerns regarding the usual PGP-powered encrypted email:
This isn't to say people should definitely stop using and promoting encrypted email, since it can be useful.
It's just it gives, more often than not, a false sense of security and can lead less proficient users to send sensitive data through this medium which isn't nearly secure enough for such use cases. Preferably, people with such threat models should opt for better alternatives, most suggested in that article (such as, but definitely not limited to, Signal, SimpleX, Matrix+Olm, XMPP+OTR/OMEMO, sharing files via MagicWormhole, encrypting with tools like age).
On a slightly tangential note, I think someone should make a Matrix client with an email client interface. I started working on a new traditional chat client (completely nonfunctional still, very much in-dev), but I've been honestly thinking more and more about making one looking like an e-mail client, where there isn't much focus on instant room-based chats, but rather on longer-lived 1-to-1 and list-like exchange of messages.