As an exception, when I post a quiz here, I invite people to email me if they want their score (to prevent answers being posted before others see the questions).
I will often then post (in the quiz thread) saying that "so and so has scored 15/20". I think that is implicit in the instuctions I write for the quiz.
If I have offended anyone by doing so, then I apologise.
However, it does offer an example where PMs are, reasonably, not kept private.