My correspondents are getting misapplied to emails in inbox. Repair folder doesn't work very long.

What is your anti-virus software?

Sorry for being tardy. Real life intrudes.

My "technical" suggestion is to manually delete the index files for that folder. It essentially accomplishes the same thing that repairing the folder does but slightly differently. Here's how:

- Right-click on the folder name and choose "Properties" from the context menu. Make a note of the Location. If it's an IMAP account it will look something like

imap://(the account user name)@(the account server name)/(local folder name)

If it's a POP3 account it will look like:

mailbox://(the account user name)@(the local folder name)/(the local folder file name)

- In Thunderbird, go to <Help | Troubleshooting Information> . Scroll down to "Profile Folder" and click the "Open Folder" button. This will open your system file browser inside your Thunderbird Profile.

- Close down Thunderbird.

- If it's an IMAP account, navigate to the folder ImapMail\(the account in question, as found in the Folder Properties above).

If it's a POP3 account, navigate to the folder Mail\(the account in question, as found in the Folder Properties above).

Here you will see files representing your various folders. There will be a pair for each folder, one with no extension, the other with a .MSF extension. The MSF ones are the indexes.

- Delete the MSF file for that folder *ONLY* - be careful to not delete any others! The MSF index file will be recreated when you next start Thunderbird. Your mixed-up headers should be correct again.

This whole business only corrects the symptom. That the indexes keep getting corrupted is the real problem. If this persists, it's a sign that there's something else going on. The most likely cause is your Anti-virus, as was mentioned by christ1 . It could also be general computer problems, such as a failing hard disc or file system corruption, although I would expect you would be having other computer problems besides just this.

Lin nailed it in the last part of his reply. The corrupted indexes are the problem. The very fact that you actually had to implement a "repair" command should tell you that something is very wrong with your database implementation. No user should have to routinely run "repair" or mess around with deleting (.msf) files buried in one's profile, except in very unusual situations.

My own experience is that this happens pretty frequently, and probably more often that I realize. The worst part is that it's a silent failure - all of a sudden emails go missing, causing me to think I've lost my mind --- "I know that email is here somewhere!" --- until I remember about "repair", which doesn't always work (it didn't fix the scrambled sender issue referred to above). I haven't tried deleting the .msf files yet, although I've done so many times in the past.

And for the record, I'm on MacOS 15.7.7, and I don't have any antivirus software installed. The rest of my system seems to be working quite well, so I'm not buying the anti-virus cause.

Fortunately for you, I'm not in charge. :-) But if I were, fixing your broken database implementation would be near, or at the top of, my to-do list. If the underlying database isn't rock solid, then it's a lot harder to take Thunderbird seriously as an email client.

And just so you understand, I'm a (pretty) happy Thunderbird user, and have been using TB for decades. I want to see TB continue its progress. But please fix your foundational structures.

Cheers, Brian

It's not "our" database implementation, it's the standard MBOX format that has been an industry standard for decades. Yes, it's somewhat fragile, not technically the "best", but it works and has the advantage of being exchangeable with most other email systems.

I believe the Thunderbird developers are working on another storage format.

If you would like to make a suggestion or feature request you can do it here:

https://connect.mozilla.org/