finding location

Dear all bidders; This project is very simple if you know what you are doing. We received an email from one of our employees. He threatens to give our secrets to competitors if we don't give him money. The problem is the identity of the person is not known. He kept his name secret. The email is sent through yahoo. We need your help to locate this person. When we trace the IP address, it goes to the servers of Yahoo. It might be a simple task to do perhaps. We will need you to help us in solving this issue. You have to also show us how you do it. The full header could be provided once you send a PM. Thanks.