It would be nice to have a standard for delivering email-like messages over Matrix, with email-like clients rather than chat-like clients. The protocol itself would support it.
Isn't the whole concept of Matrix to be a DAG of messages with hashes for tamper-resistance (ie a Merkel tree) to secure the history in the presence of many servers, some of which might exhibit Byzantine failure?
What is the point of any of that for 1-to-1 communication?
It's a general Merkle DAG, not a tree. This is because two homeservers can append nodes to the DAG at the same time. The state resolution algorithm ensures all homeservers in a room eventually agree on a consistent state despite receiving nodes in an inconsistent order
It's fairly useless for 1-to-1 communication. But for any group communications, it means there's no one server that can go down that will take down the whole room (unless all the participants are on the same server); contrast with XMPP MUCs.
All of a user's device still go through the one "homeserver" which is the only party doing the federation. If the multi-party stuff is client-to-server, again the Merkle tree is useless.
