Just had the most recent upgrade to Thunderbird. I now get a microsoft message when trying to download new messages, saying it cannot access an invalid certificate. Prior to this upgrade, I had to manually validate the certificate for my email provider every time I re-opened THunderbird, or tried to send outgoing emails. Although inconvenient, this system worked and I could use the email provider system. Thunderbird will not download any emails now or give me the usual error message that I can manually override to get emails to work. The mail server is: mail.besttelecom.net.au