Hello again, We were in contact yesterday regarding the problem after upgrading the Thunderbird to version 78. I can't still send, receive, save any messages. You have suggested to check the security protocols but my provider says that everything is correct. They work on TLSv1, TLS1.1 oraz TLSv1.2. Everything works fine when I log through the web page. But Thunderbird pops up with some issues: "sending the message has failed. Communication participant's certificate has an invalid signature. The configuration needs to be corrected" or something like this, when trying to save the message: "it's not possible to copy the the draft of the message o the sketch folder due to network or file access errors" I would really appreciate Your answer, Anna