Most states have stalker laws if it gets really bad. I would keep a record and file his emails, just in case. It is important to take precautions. The fact that he is still bothering you after three years suggests that he is a problem. You can get a restraining order as well if he threatens you in any way. I am not saying any of this is necessary but you should be prudent and keep aware that there are legal things that you can do if you need to.