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If the messages appears on the desktop and stays longer then 2 minutes on the desktop screen for sure something's wrong with the configuration. do you have used more email programs combined with thunderbird?If you use these email software togheter be sure that they have the same security configuration as the configuration in the software .Be sure the security certification is oke.remove old certifications or other certifications that thunderbird has accepted and check carefully if they are no good anymore to stay there and or does not belong there to activate .removing old certifications at thunderbird.go to settings and choose security and privacy )certifications)choose servers , do remove them all .start up the thunderbird program again.Try to get the inbox messages to download and read the drop down message and fill in to accept that certification s trust of them again in the drop down field choose the option to fill in the option permanent and click on accept .also the use of the vpn service can be turned off to experiment with it.only if that is possible to do.thank you

Greetings Firefox volunteer

You had no trouble with 128.5.0?

• Start Windows in safe mode with networking enabled - https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode
• Still In Windows safe mode, start Thunderbird in Troubleshoot Mode - https://support.mozilla.org/en-US/kb/troubleshoot-mode-thunderbird

Does problem change? Pop accounts or imap accounts?

Please post to let us know