S/MIME Signing and Encryption

First, try updating to the latest test release: https://updates.mailmate-app.com/archives/MailMate_r6062.tbz

Depending on the revision you are using now, you might get a better error message in the composer window which can point us in the right direction.

I went from 5973 to 6062.
The message stays the same. Since I did not include the details when I opened the call here they are:

S/MIME: Failed to sign the message
Log S/MIME sign
Sender robert@somedomain.xy
Suggestion Verify that you have the certificate necessary to sign the message.

I do have the necessary certificate in my keychain so I am a bit puzzled.

Ok, try again after enabling this hidden preference (debug output isn't as good as it should be for S/MIME, but it could provide a bit more info):

defaults write com.freron.MailMate MmDebugSecurity -bool YES

Make sure the certificate is valid and trusted.

Did that. I would have expected that there will be some output in /tmp but there is no /tmp/*mailmate* debug file present.

No, the additional output should be in the same place as before. Just expand the “Failed to sign the message” error message.

ok. Now I see it has changed ...

Log S/MIME sign
Searching for certificate of identity with address “robert@somedomain.xy” for signing
Searching default keychain
Looking for candidates (robert@somedomain.xy)
Found 3 candidate(s)
Searching all keychains
Looking for candidates (robert@somedomain.xy)
Found 3 candidate(s)
Sender robert@somedomain.xy
Suggestion Verify that you have the certificate necessary to sign the message.

Hmm, my keychain only shows one (valid and trusted) certificate for that email address.