Wikipedia
Bitmessage is a decentralized, encrypted, peer-to-peer, trustless communications protocol that can be used by one person to send encrypted messages to another person, or to multiple subscribers. Bitmessage encrypts each users' message inbox using public-key cryptography and replicates it inside its P2P network, mixing it with inboxes of other users in order to conceal user's identity, prevent eavesdropping and allow the network to operate in a decentralized manner. The Bitmessage communications protocol avoids sender-spoofing through authentication, and hides metadata from wiretapping systems.
In June 2013, the software experienced a surge of new adoptions after news reports of email surveillance by the US National Security Agency.
, the network processes several thousand private messages per day.