An SMTP compat "mail" client that uses Ceramic documents to sync & relay mail-like messages between identities. Roughly related to did-comm.
The fundamental idea of a self sovereign identity is the "DID", a decentralized identifier, looking like did:key:zkmanycharacters
. DIDs are uniquely identified by key material of an user, derived by some random seed only the user knows. DIDs can be resolved / expanded to DID documents that contain information about the public keys a user uses for communication and authentication purposes.
At its core, the Ceramic protocol uses DIDs to represent identities that are interacting with documents, atm did:3 and did:key are supported: https://developers.ceramic.network/learn/overview/#authentication. On top of Ceramic, IDX is adding a layer of well formed documents that contain additional information about the user, e.g. an user "profile".