for hotmail users, go to option>mail tab>mail display settings...
select advaced radio button in Message Headers section..

it shows something like this:

"When reading a message the Basic setting displays the sender's and recipients' names, the date, and the subject. The Full setting displays additional routing information that may be useful for tracing messages. The Advanced setting displays complete MIME headers (for power users)."

most of email services have this kind of option.. find them, and u can trace them with the listed routers and IP addresses... BUT hard to trace peoples who use proxy..