Comment 26 for bug 154145

(In reply to comment #21)
> But, again, after I rename that folder to something without spaces or odd
> punctuation marks, it comes back after I reopen the program.

This is not a user support forum but lets give a little help. You should rename this folder or MBOX file outside of Thunderbird. Close the application, rename the appropriate files/folders and delete the .msf file. After the next restart Thunderbird should come up with the new name and creates a new summary file.