Sorry if this is yesterday’s news to you all, but I just found out about this Android app that makes it easier - as in, less steps - to encrypt and send any message in a highlight-copy-paste fashion, with automatic integration in several e-mail front ends.

It still receives security updates and the repo is still maintained, but the app is no longer being actively developed to add new features. https://github.com/open-keychain/open-keychain