I would suggest that the Refresh button should clear “Read” items from the “Unread” folder as well as downloading new messages. This would reduce the need for the user to laboriously select another folder and go back to the unread folder in order to declutter it.
I think this is a stupid idea!
Refresh is just a way to manually force a sync with the server. It would not be practical every time eM Client syncs with the server that previously unread messages were marked as read. How would you then know which messages you have not read?