Eating cockcheese smegma

I'm gonna switch to English, this may be easier. Thanks for your help first of all.
The above structure is not the case. Strangely, the folder structure in Outlook looks as always, only one inbox, one sent items etc...and one folder for each subject in my archive. So the duplicate structure that is shown under Settings/General/Storage is only visible there. BUT: in my source folder structure I have now duplicates everywhere, up to 10-15 times the same email across whole conversations. This is what's eating the storage space. And having to go through this manually to delete each duplicate email would take years...
I really don't know what to do - looks like I shot down my whole cloud mail system. :-(