claws-mail-smime-plugin 4.1.0-2 (amd64 binary) in ubuntu kinetic

 This plugin handles S/MIME signed and/or encrypted mails in Claws Mail.
 You can decrypt mails, verify signatures or sign and encrypt your own mails.
 .
 S/MIME is also known as PKCS#7 and uses the application/pkcs7-signature
 or application/x-pkcs7-signature MIME subtype within messages.
 .
 Receiving an attachment called smime.p7m is also sign of this kind of
 signature usage.