Install kuvert by entering the following commands in the terminal:
sudo apt update sudo apt install kuvert
Description:
wrapper that encrypts or signs outgoing mail
kuvert automatically signs and/or encrypts outgoing mail using the PGP/MIME standard (RFC3156), based on the availability of the recipient's key in your keyring. Other than similar wrappers, kuvert does not store key passphrases itself, ever. kuvert works as a wrapper around your MTA but can be fed mails via SMTP, too.
Homepage: http://www.snafu.priv.at/mystuff/kuvert/
Version: 2.2.2
Section: universe/mail