As per Sparky621's comments.
The bottom most "Received from:" section contains the network IP address that sent the email.
By performing a lookup on that IP address in a regional registrar database, you should be able to find the network abuse contact, which is normally abuse@domain. A good free tool is
http://geektools.com/whois.php.
The top most received from section usually contains your networks mail transport address, this will not be the sender of the email.