Obviously you thought you knew better and modified the default locations for mail. Probable did something fatal like choosing to use the documents folder and causing issues with file contention from your antivirus product. There are a number of locations which Thunderbird simply refuses to use to store messages because doing so is dangerous to your mail data. There is a support document on the site that I put together back in 2019 that explains it, so I am not going to reinvent the wheel by repeating myself. See https://support.mozilla.org/en-US/kb/dangerous-directories-Thunderbird-account-settings So I guess the first issue is to identify what account data you have located in a poor location.