In a short answer, no, you cannot trace an email sent from behind a proxy, since the originating IP address in the headers will be that of the proxy. In a long answer, yes, you can trace beyond the proxy, but not without viewing the access logs of that proxy server, and the one before it, and the one before it, etc, which you will not be able to legally do without permission or a warrant. Canned software packages cannot do that for you, since they would have to actually bypass the access restrictions (i.e. hack) to those logs.
I am not sure why this is considered "ethical hacking" But yes, there are programs out their that can trace your IP, but if you run a good enough Proxy then you will be fine.
