MailHops

MailHops API uses GeoIP and Reverse DNS to return IP location, distance traveled and host name. The example response on the right is a JSONP response from the API.

The IP addresses (Hops) were parsed from the Received: headers in an email that I got from Twitter.

As you can see the email went from Twitter to Google then I received it in Denver.

Then you can do cool stuff like map the route of the email or add filtering rules. Say, spam messages that are routed through China.