It is not first time my WLM get corrupted and my messages get messed up or even gone.

The customized file structure under Storage Folders is gone completely and only default folders visible.

The other folders are duplicated with  and marked with (1) in folder's name.

How can I manually restore the file structure, eliminate duplicate folders create (if not restore) the folder tree under Storage Folders?
I tried to do that like with the normal folders will do under File Explorer but the folders I added are not shown at all.

Please help,

/jas

Note:

I cannot use Import Messages option because of this error:

The folder is valid, and using File Explorer I can see that the folder contains several sub folders containing the email messages.

/jas

Original title: What is the WLM file structure?