Mail and Exchange (FILE folder!)

Hello,

i have a problem with Mail and a MS Exchange account.

In particular, the Exchange account syncs on Mail a folder called "FILE" full of incompressible message with no sender email. They increase by using Mail, but i don't know how they come.

The problem is that when i make a search the result is polluted of these useless and annoying emails.

I tryed to delete them but by using mail they come back.

I tryed to configure the Exchange account as IMAP but on folder list appears a lot of other folders (like: contacts, calendar, sync error, etc...) that don't help to make my email app simply and easy to use... (unsubscribe folder don't work, the folders list is blank)

I hope someone can help me!

Massimo

OSX 10.11.6 - Mail 9.3