Finding the location, identity, or affiliation of email senders

kuro5hin.org: "Thanks to wireless networks, internet cafes, and web mail, it is now common to send email from just about anywhere. So, where was that friend, coworker, or stalker when she sent that message last night, and what else can we learn about her? Using simple techniques and a few well known, but often-overlooked email headers and internet tools, it's often easy to find out.

Likewise, the email you send may also include your location and school or employer, even if sent from a personal account. Do you or should you care? "