Over in the enigmail mailing list:
Patrick Brunschwig writes about converting an encrypted message into a cleartext
If the message was signed and encrypted in one step, then the signature
will be removed as well. GnuPG does not have a functionality to extract
the signature from the encryption (which would theoretically be
If this functionality was provided, then enigmail could presumably preserve
signatures on the transformed message.
I don't personally think this is a high priority, since i think a better
approach (over storing the message as cleartext) is to simply cache the session
key to facilitate future decryption without secret key access.
But i wanted to record the observation of the missing feature here.