It depends on the method the sender used. If they used an encrypted, anonymous email service, then it’s virtually impossible to find out the identity of the sender. If they simply used a fake name, you could try checking the email’s header information to try to find the IP address the sender used, which could give you clues to who sent it. However, often the IP listed is the IP of the email provider, which won’t be helpful. The sender’s internet service provider and email provider both can know the sender’s IP address, and a court could order this information be revealed.