My sympathies. I have a friend like that, so I know the stress it brings out having to control yourself from beating them to within an inch of their life. There's a program out there called mailwasher. Get it.
It allows you to bounce back any email to the sender, as if the edress to which they sent it was invalid.
I don't know if you've told your friend to stop sending you emails like that, but in the event that you have and they still won't stop, mailwasher is a great program. All their shit just bounces right back to them. It's also great for getting your name off spam lists as well. Spammers don't like bounces and will delete your name from their list as a result.
If that fails, take a bible, and beat him about the head & face with it, until his lips swell up too big for him to preach