How to trace an email sent to you?

We get lot of spams from everywhere on the net. We also get some suspicious mails containing viruses. But how do we trace it back to who actually sent the email? Ofcourse its hard to pin point who actually sent it. It will be nice to know where the email came from (which ISP) so that we log a spam call to have the sender's account suspended.

Here is a brief document on tracing an email. This document explains how to enable email headers in most of popular email clients and online email providers such as Yahoo, Google, Hotmail etc.