I am struggling to use the windows search function for emails within Thunderbird's mbox files. The windows search function simply doesn't work with TBP.
In the settings of Thunderbird, there is a button that will allow the windows search function to search within emails, as well. I can check the checkbox, but after I restarted TBP, the checkmark is gone. I have tried this in Windows 7 and Windows 10, with various TBP versions down to v24... and always had the same issue.