Outlook 2016: deleted Folder keeps re-appearing

[mmo]

A while ago (more than 2 years actually) I deleted a folder in Outlook by moving it into the Trash (the Trash of the corresponding email account that is, not Windows' trash).

Odd enough, regardless of how often I already emptied that account's trash this Zombie-folder re-appears about 5-10 seconds later. It is empty, but the folder re-appears.

The account where this happens is an IMAP account at my local phone provider. That folder is NOT visible when I access that mail account via the Web-interface, i.e. it seems to "live" (and survive) only in Outlook.

I can move that folder out of the trash (then it behaves like a normal folder) and I can delete it again. At this point I then have two of them (the second with a ...(2) suffix). After emptying the trash the new one (that with the suffix) is gone - as one would expect - and remains gone, but the original one (that without the suffix) is at first gone, too, but re-appears about 5-10 seconds later.

Any idea, why this is so and how to finally beat that folder to death once and for all?


Oh - since these will invariably come as suggestions:

* I have jumped through that scanpst.exe loop already! Didn't fix it.

* And - no - I won't delete and recreate my email account in Outlook just for that.