You might point out that that if the emails are intended for public consumption, they could be considered defamatory and if they are only personal, they are harrassment and, technically, assault.
This person needs to turn down their anger level and/or tone down their language or you will refuse to even read their emails so there will be no point in them even sending them.
Tell them you have now accumulated enough evidence in emails from them to make it worth taking action.
Or you could do what this FlatChatter did HERE and let everyone know exactly what is being said.
Best of luck with what is a nasty situation