This Trace Email tool can help you do precisely that. It works by examining the header that is a part of the emails you receive to find the IP address.
To trace the IP address of the original email sender, head to the first Received in the full email header. Alongside the first Received line is the IP address of the server that sent the email.
There are instances where tracing an IP address through the email header is useful. A particularly irritating spammer perhaps, or the source of regular phishing emails. Certain emails will only come from certain locations; your PayPal emails won't originate in China, for instance.