http://nguipxnkrp3qrzrlduhsatpcpwehnblzmlkc5ifiumxq4z5jlh4lwvid.onion/os_archive/os_hidden_mail.html
The great thing about this system is that it is opensource, distributed, anonymous, transport layer encrypted, and the message is RSA 4096 encrypted by gpg. Currently you do not have to have a working server to submit mail to a server. So if you were part of a 10 man spy ring with a central node the field agents only need to learn how to use gpg to encrypt and to install swaks , tor ,...