I use Microsoft Outlook for Windows from time to time and discovered it is possible to sign/encrypt emails with an S/MIME certificate even if the email on the certificate does not match the "From" email address. Although this is disabled by default, it can be enabled by following these steps: https://learn.microsoft.com/en-us/previous-versions/troubleshoot/outlook/how-to-turn-off-email-matching-for-certificates I wonder if there is an equivalent mechanism for S/MIME and/or OpenPGP certificates imported into Thunderbird, whether by changing settings in the config editor or otherwise?