We had a situation once where a user shared content to a lot of other users which resulted in some complaints so you might switch on "Require User Connection" - Require users to be connected to recipients of direct messages and shares. Used to prevent spam.
But I don't think it's going to happen much. Put something in your House Rules that it is not good etiquette. And anyway you really need your senior leadership backing this and getting involved - engagement is a good thing. Presumably there are no blocks to stop employees emailing senior leadership or button holing them in the corridor? Why do you think 'this' behavior will change (much) given a new platform?
I liked how the CEO actually responded every time (less sure about the pink rabbit costume but heh...).