Start Thunderbird in <b>Troubleshoot Mode</b>. The following article explains how to do that and why it can be useful to help identify the cause of a problem: https://support.mozilla.org/kb/troubleshoot-mode-thunderbird What's your operating system? If Windows, start in <b>Safe Mode with Networking</b> mode: https://support.microsoft.com/help/12376/windows-10-start-your-pc-in-safe-mode Does any of that cause the problem to go away?