SUMMARY When sending a signed email in the S/MIME format, the email is marked to have "invalid signature" when read. If instead S/MIME opaque is selected, the signature is recognized valid by the sender account, invisible by others. STEPS TO REPRODUCE 1. Select S/MIME signing mode from settings 2. Set an X.509 certificate for signing 3. Send signed email OBSERVED RESULT When sending a signed email in the S/MIME format, the email is marked to have "invalid signature" when read. If instead S/MIME opaque is selected, the signature is recognized valid by the sender account, invisible by others. EXPECTED RESULT Of course signature should always be visible no matter the recipient, and valid no matter the signing format. SOFTWARE/OS VERSIONS Operating System: Fedora Linux 35 KDE Plasma Version: 5.24.4 KDE Frameworks Version: 5.91.0 Qt Version: 5.15.2 Kernel Version: 5.16.5-200.fc35.x86_64 (64-bit) Graphics Platform: X11 Processors: 8 × Intel® Core™ i7-8550U CPU @ 1.80GHz Memory: 15.5 GiB of RAM Graphics Processor: Mesa Intel® UHD Graphics 620