I would have thought this was probably descriptive of the process. https://support.mozilla.org/en-US/kb/archived-messages

Thanks Matt. Everything in the support document works as intended. However, I was talking about sent emails, emails I have sent as reply or as initial emails. But I got confused by another error which is connected to this. It is not the sent emails that get misplaced, its the inbox emails that I archived. Which I'll try to explain now:

I have to translate this from german since setting Thunderbird to english for me changes only the language in the setttings dialogue itself and not everything else. If I select Account > Copies and Folder > Save Archive as > Folder "Archive" in: local folders it doesn't "stick". It defaults to some folder that is on my IMAP server, i.e. not a local folder It never saves emails I "archive" to a local folder on my harddrive... except for my "sent" emails. Sent email I find in:

Archive

 ⎿ Local Folders
   ⎿ Year
     ⎿ Year-Month
       ⎿ Sent

I expected my inbound emails to show up in that file structure as well, but they don't. Any ideas on how I can correct this?

I think I'll abandon this question and open up another one with the correct/updated information. This is the new support question: https://support.mozilla.org/en-US/questions/1361760

Edit: After some trial and error I found the correct solution to my problem in this question: https://support.mozilla.org/en-US/questions/1115180

Please do not ask duplicate question. It just makes a mess. So I will lock this one.