Since some time some folder names in my mailbox have been "wrong" in Outlook. What do I mean by wrong? Well, they had names like "Junk-E-Mail1" and "RSS-Feeds1" and I could not rename or delete them (because these are "default folders").
Also I had a mix of english and german folder names, because I had once a german mailbox, then this was migrated to Office365 and then I used to switch between german and english versions of Outlook.
Kindly, Outlook offers a solution for fixing "wrong" folder names very easily by restoring the "default names" for them.
This can be done by executing the command
To ensure that outlook is found, locate the outlook.exe file first - in my 32bit version Outlook 16 is stored in
C:\Program Files (x86)\Microsoft Office\root\Office16.
Now my Inbox is correctly named "Inbox" (instead of "Posteingang" because I'm using the english version of Office now) and the "wrong" folder names are fixed as well.