Tor Mail is an anonymous email service running on the Electronics Frontiers Foundation Tor anonymity network, Tor Mail is an independent project and not endorsed by the EFF, it works as a hidden service inside the network, a hidden service protocol needs to advertise its existence before people can find it, it does so by sending its public encryption keys to introduction points, everything is proxied in a decentralized way which causes delays but secures your online anonymity, the advantage of a Tor hidden service is that the server location can not be found this makes it impossible to seize that server and keeps the user and the server operator identities safe.
After signing up for Tor Mail you will get a @tormail.org email address where people can reach you, messages can be accessed through Webmail, SMTP, POP3 and IMAP, Tor Mail is composed of several servers relaying email in and out of the anonymous Tor network, no logs or user information is stored, the developer claims that they will not help anyone to identify users and since they hold no data any subpoena forcing them to do that would be useless.
How to access Tor Mail
The only way to sign up for a Tor Mail email address is through a .onion URL (http://jhiwjjlqpyawmpjx.onion/) , a .onion website is a 16 character long alpha numeric URL Base32 encoded 80 bits long automatically generated by a public encryption key, .onion has been designated by Tor to identify hidden services, you can only access it if you have Tor anonymity software installed in your computer, using the Tor network to browse the Internet not only will hide your IP but also get around ISP Internet filtering and monitoring, someone watching your activities online will not be able to see or log what you are doing other than connecting to a Tor network server.
If you do not want to install Tor in your computer you can use a live DVD like Tails. To find out about more Tor hidden services like IRC networks, Wiki, SSH server, Usenet and others, visit Anarchopedia list of Tor network links.
Visit TorMail information homepage
UPDATE: August 2013>> Tormail hosting admin has been arrested