OpenPGP digital signature unverified
I have an external PGP key on a Yubikey that has three identities (e-mail addresses) on it.
I can send an e-mail from one of these identities to another. If I encrypt the e-mail the other mailbox will be able to decrypt it and verify the signature (of course). If I only sign the e-mail, however, the other mailbox will complain, "Invalid Digital Signature". The 'sent' folder of the sender will show the e-mail as correctly signed even when it was only signed and not encrypted.
Any ideas what is going wrong here would be gratefully received.
Alla svar (1)
To add to this confusion, it is only one of the three identities that appears to have the problem. The other two can send digitally signed e-mails that will be verified by all three identities.