Try doing Folder > Properties > Repair on Inbox. If that doesn't help, start Windows in safe mode and Thunderbird in safe mode too. - win10 https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode That are your results?
Bug 1560037 Comment 3 Edit History
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Try doing Folder > Properties > Repair on Inbox. If that doesn't help, start Windows in safe mode and Thunderbird in safe mode too. - win10 https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode What are your results?