>> Funny you should say that. Also how is that any different from registered mail or any other method where it's guaranteed that a message was sent.
> There's no proof that they were communicated with by merely posting to f.b.
With registered mail, there is proof. That proof is physical and is mailed back to you and is suitable for 3rd party verification. You can actually verify that the person that signed for it is the individual in question.
NONE of that exists for Facebook.
Posting something on Facebook is only vaguely like publishing it in the local newspaper (also bogus).