Kleopatra doesn't show any information about the recipients of S/MIME-encrypted data if the public S/MIME certificates that were used for encryption are not present. (Noticed while working on T7981: Kleopatra: Show "No secret key" error for S/MIME protocol.)

Since gpgsm doesn't return any information about the recipients (although it should know issuer and serial number) all we can do is display something like "Recipients: Unknown"