Can receive but not send email in Thunderbird. Get the send message error "Sending of the message failed. Certification key usage inadequate for attempted operation. The certification related to 127.0.0.1 must be corrected." Am using Thunderbird on only one computer, running Windows 10, with the Proton mail bridge, which appears to be working correctly on other computers/devices, can send email through other programs as usual with same email addresses. Am totally unfamiliar with this error, really don't know what to do or what to check or how to diagnose. Have tried booting in safe mode, have disabled ESET antivirus, no effect. I do not have an IT department. Any suggestions greatly appreciated.