You can turn off P.M.s (private messages) if you are getting harassed that way. Sadly though if you already corresponded with someone via P.M. they probably have your email anyways.
As for on this actually board I would recommend contacting an admin and seeing if they will delete the user/ban the I.P. address. Before you ask for this though make sure it is worthy. Note that there is a difference between difference of opinion (Why do you buy graded bullion!?!?!? Dumb!) and something more, non-family friendly.