Updated to 88.0.1

There is no such version. In general, v88.0 is a beta version intended for testing purposes, but not for production use. Is this why you installed a beta version?

Read online that probably needed to go to properties for the In box and select "Repair Folder". I did and now I have lost all emails in my In box older than May 2, 2021.

What is your anti-virus software?

It sounds like your mail files got corrupted. Depending on the state of corruption using "Repair Folder" may erase messages from the affected folder which cannot be recovered anymore. In other words, the damage was already done, and by using "Repair Folder" Thunderbird did attempt to repair the damage and get mail files back into a consistent state. In that case you'd need to restore the lost messages from a recent backup done prior to the corruption.

Corruption is often caused by anti-virus software messing with Thunderbird mail files. It is therefore recommended to create an exception for the Thunderbird profile folder, so that the real-time scanner won't attempt to scan the profile with your mail.

For more information on the profile location see http://kb.mozillazine.org/Profile_folder_-_Thunderbird

Also see http://kb.mozillazine.org/Keep_it_working_-_Thunderbird

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