Reporting spam to your Internet Service Providers helps reduce it, but your email software might not provide you with all the necessary information to track down the online offender. Fear not! Stopabuse.org lists instructions for fleshing out email headers on dozens of email programs.
"Full headers that contain the entire path and the route the email or newsgroup message took are absolutely required when sending complaints about spammers, online harassers or cyberstalkers. If you do not have an email program that has the ability of showing full headers, it's highly recommended you switch to one that does. Without full headers, the ISP is unable to track down a spammer or online abuser."