I just discovered that my supposedly anonymous e-mail isn't so anonymous after all. My IP and host name is sent with the headers. This information exposed, what can be found out?
All sorts of things -- what OS your machine (or router -- whatever's directly connected to that IP address) is running, what services might be running on there, anything that can be determined by talking to the services provided on that IP address (Windows file sharing is the best one, but even a mailserver or FTP server can provide all sorts of info).
More broadly, that IP address can be correlated with other connections you make (to websites, other e-mail, etc) as a weakish identifier.
What kind of a bollocks anonmailer doesn't strip incoming received headers, though?
A few things, with some optional depending on some variables.
- Your Location - Nation definitely, State probably, City sometimes.
- Your ISP - its name, who owns the IP address.
You can get this information on your IP at MaxMind.
Also, since they have your IP address, they could scan and probe your network - so if you have a PC directly connected to that IP address without a firewall they could potentially find out a ton of information about you; however if you are behind a firewall, and as long as they do not compromise that firewall, then you are pretty safe from this end.
Finally, somone could go to your ISP to find out more information about you (Your name, address, hours connected with that IP, etc) but this varies by law and in the US you need a subpoena or other "emergency" reason for this info.