Threatening Email

Hi,

I just received a very threatening email from a girl with a Yahoo email address. It was the worst, most vulgar, thing I've ever read. She aslo threatened my life at the end. She signed up for my newsletter and received todays issue and for some reason went nuts. The message sounded very sick and even demon possessed I think I can easily say. I went to the Yahoo website and searched and searched for an email address that I could send this to, so that this person would have their account cancelled and so they could follow up with the Police or something - after all, Yahoo would know her address. I couldn't find any email addresses at Yahoo.

Has anyone experienced this before, and what can be done ?

Your help is appreciated. Thank you.