Thunderbird: Inbox mail data corruption

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Today, I've experienced strange things on a computer running Thunderbird:
New, incoming mails seemed broken:
- Some didn't display at all when selecting them
- others displayed the content and subject of another email

There's a nice article about known problems that might occur with Thunderbird:
Thunderbird issues: Disappearing mail

If it's something more severe, this article might help:
Compacting doesn't seem to work

It surprised me that "compact folder" didn't mean that Thunderbird would zip a folder to save space, but that if you don't regularly compact a folder, it is more likely to get corrupt one day (especially the Inbox).
Here's an article about what to do to "Keep it working".


My case was a bit trickier - and in fact really ugly:
It seems that the Inbox was completely corrupted, allowing only 2 emails to be displayed at all, although it contained approximately 1700 emails in total. I tried copying the files to a newly created folder (as suggested in the articles above), but the mails could not even be copied. It said something like "copying 1700 mails...", but only a handful arrived at the new folder - and only 2 of them could be opened. Just like before.

However: I was frustrated and right-clicked on the Inbox and selected "Compact". Well... The Inbox was empty afterwards, leaving only 2 mails: Exactly the ones that could be opened before. Seems that the rest was pretty broken. I've still got a backup, so maybe I can restore them somehow. We'll see....