kuvert - 2.2.2 main

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.