I normally do not want all outgoing mails to be signed with my S/MIME
certificate but only if I add a special tag to the subject (e.g.
"[sign]"). So I have enabled the "Only sign when encrypt" option.
However, it seems that even I add the tag to my subject, the mail will
NOT be signed.
Is there a possibility to sign the message without encryption just on a
case by case basis?
The reason is, that I want to sign a message explicitly if I want to
send a recipient my S/MIME key before we both have exchanged the keys
and would be able to encrypt the message.