To restore corrupted mailboxes:

1. Exit Thunderbird.

2. In your profile folder, open the Mail subfolder, and then the subfolder for that mail account.

3. Delete the *.msf file for the folder (mailbox) that is giving you problems-- e.g., if your inbox is the one with problems, delete inbox.msf. Do NOT delete the file named Inbox (with no filename extension), as it contains your messages.

4. Restart Thunderbird. It will analyze your message file and rebuild the index file (table of contents) from your existing messages.

To help keep your system healthy after you get it working again, compact your mail folders regularly, and move messages you want to keep out of your inbox into their own mail folder.

On Linux, the path is usually ~/.thunderbird/xxxxxxxx.default/

helena@mora:~$ rm ./.thunderbird/xtyyb7lf.default/Mail/"Local Folders"/Inbox.msf