Been using thunderbird for at least 20 years, and learn to live with the bugs and wait for the next release waiting and expecting the issues of the previous release were solved in the next one. I've been using S/MIME certificates for many years without problem. I've recently installed a new certificate wich is correctly installed in my personal repository expiring in 2027. Since version 141 this certificates shows as selected, but is not used. Updated to release 142 ... but the problem persists. I'm attaching a screen capture were shows the error message and the Developers Console showing the exitcode when trying to send a mail with digitally signed. Please also note (i don´t know if this is related or not) that when y check the certificate in the account the hexadecimal ID of the certificate is not shown. If I clear the certificate and select it again it is shown in this screen. Attached to this you can find a capture of what mentioned before. Please let me know if more information is needed. Thanks / Regards Ariel Pereira