First of all you need to find the IP address of  where the email originated from, you could find this IP in the email header section, in some webmail you have to click on a link such as show details to see the header section. After finding the IP address you could trace this IP to find where it is located.
To find out exactly where that originating IP address is, all you need to do is perform a location look up on the IP address. you could go use many websites to do this such as this one