Interesting, I just did a repair on some of my Inboxes to see what happened. It brought back in all the messages that had been moved by rules which I thought odd. Running the rules again moved the messages back, so fingers crossed this has fixed the problem or at least helped.

Do you have an antivirus scanning mail? They are the most common cause of multiple downloads of the same group of mails on POP accounts. THe download start, the antivirus encounters a malformed email and basically drops dead, so the session sits, until it times out and the next fetch becomes the same old same old, until it encounters the same malformed mail and goes on repeat.

Some folk have had success in this by simply deleting the contents of the web mail spam folder as malformed emails are usually also identified as spam server side. if that does not work for your disable the email scanner until your outstanding mail is downloaded successfully. You can re-enable the scanner after that if you are happy playing roulette with when you will see the issue again. Or like me just don't scan email. I see it as more trouble than it is worth.

Thanks Matt.

No I don't have any anti-virus scanning the emails as they download. A certain amount of filtering is done at the host, then TB downloads what's left. I get a lot of spam in several mailboxes, but TB's spam detection works well so I don't bother with anything else.

I have been trying to go through repairing my mailboxes, then downloading mail again. It's strange that if I do a download, there are only new messages to download, but if I wait, TB seems to download the old ones again on it's scheduled check for new messages. Nothing has changed on my system or at the host, except I allowed TB to update to the latest version.

Hoping I can resolve this somehow and crossing my fingers the mailbox repairs do the trick. It's getting frustrating and my email backups are taking longer as well.

Having repaired all my email folders and left it a day, I think most if not all of the email accounts are now fixed and I'm not getting duplicates downloading any more, so I'm going to close this ticket.

Having had as many as 20 copies of each message in some folders, it's a mess to clear up and I'm going to leave it to time and my "delete after 7/14 days" policy to clean folders up.

So I think the new TB is working ok, it just decided to corrupt my folders when it installed. Fingers crossed.

Sadly the latest release (102.4.0) hasn't fixed the problem, it's just as bad.

I'm getting emails downloaded twice, plus any read emails left on the server are downloaded again when the scheduled inbox checks run. If I manually run Get Messages on an account it mostly only downloads new messages, but the scheduled email retrieval seems to download all the messages from the server again, even though they are marked as read on the server.

I have seen a number of other reports of the same or similar problems so strongly suspect it's not just me.

I'm running TB 102.4 currently on fedora 36, kernel 5.19.16. I've been running this configuration since 2014 applying upgrades as fedora repo releases them. I do have multiple email addresses configured for download but only one has this issue. But it is an issue on my laptop and on my desktop, for the same server but different email addresses.

... pardon my skip there. I claimed only one email has the duplicate message issue but when I wrote it out I realized it was one server but different email addresses. The server is gmx.com.

well, since I couldn't remember when I last deleted the popstate.dat file for the affected email address, specifically was it before or after I ran the latest TB update, I decided to try deleting the file again. That was late yesterday and it's beginning to appear the duplicate download issue is not recurring.

The problem is now solved and it wasn't anything I (or we for others with the same problem) were doing. It was a Thunderbird bug and it's been fixed according to the release notes for 102.4.2, I can confirm that for me at least things are back to normal. No multiple downloads of the same emails from the server time and time again and my email folders are returning to normal. If you haven't updated to this version and have the problem, I recommend doing it now and fingers crossed that should be your problem fixed too.