kuvert 2.2.1 (s390x binary) in ubuntu bionic

 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.