@[email protected] I went with Proton and the reason was either that I could import and use my own PGP key, or because it had more general compatibility with other mail services using PGP (well possibly both those reasons). So I could send encrypted mails to Thunderbird users as well as GMail users (who had a PGP encryption extension).
@[email protected] maybe something like Tkman at https://sourceforge.net/projects/tkman/? Or web based like https://linux.die.net/man/ or https://man7.org/linux/man-pages/index.html.