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I just installed Thunderbird 3 on my Mac. Often when I click on an IMAP folder (other than the Inbox), Thunderbird will suddenly and arbitrarily mark unread numerous messages (from several to thousands) within the folder. I issue the "Mark Folder Read" command, which has the desired effect... until I click the folder again. The number of messages marked unread seems random. What could be the problem? This does not happen on my work computer, which runs Thunderbird 3 for Windows.

Edit: I have noticed recently that Thunderbird 3 for Windows has a tendency to mark messages unread as they are archived.

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Do you use a gmail account? Because the difference between gmail tags and thunderbirrd folders could create inconsistency... – fluxtendu Feb 23 '10 at 16:59
Nope, FastMail. – anon Feb 23 '10 at 22:22
nothing strange about the permissions on the library folder? (I guess "library/application support/thunderbird"). tried deleting that folder and restarting from scratch? is thunderbird doing something in background, like downloading more messages, while you use it? – o0'. Feb 24 '10 at 10:31
I have noticed a lot of activity in the background. I will check these things when I get home. – anon Feb 24 '10 at 14:23
up vote 1 down vote accepted

It seems to be a bug in Thunderbird. First try updating Thunderbird to a more later release.

Also I found this blogpost after some searching. Maybe it'll work for you.

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(Very good find!) – Arjan Feb 28 '10 at 10:07
Nice sleuthing! I couldn't find anything on this. – anon Mar 1 '10 at 14:24

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