After extensive testing and talked to your support it seems like Deskpro does not support setup to an exchange public folder through EWS. It also looks like it cannot access subfolders of a users inbox when setting it up to read from specific folder. Only folders contained in the primary hierarchy seems to be supported. As EWS support access to and controlling public folders it would be a nice feature if this could be implemented. Atleast support for subfolders in a inbox hierachy and not only the root of the mailbox.