Case A - new/unread messages in inbox:
Case B - NO new/unread messages in inbox:
Of course other ideas for the wording/whatever are welcome - as you can see I choosed to display a link to "Private messaging" for my board and only a notification in case there is a reason for. Another advantage is that it's harder to miss a new message by overlooking the count number (the visual change is way more more obvious if "private messaging" transforms to "x new messages"). All in all I got a positive feedback from my board users for this tiny but usability-effective change.