Insulting email from another graduate student
I cannot give you advise on what to do in this situation as it depends strongly on the context, and you cannot give that information on an open forum like this. 

However, I can make one comment: in general I would never try to solve such a conflict through email. Email is great, but when you sense that a conflict might start you immediately need to stop using email and try to speak with the person directly. Small misunderstandings that are easily resolved in face to face communication tend to get blown out of proportion very quickly in an email conversation.