Agreed. In fact, if consistent E2E encryption could be assumed, then the proxies could be implemented as simply a dedicated address on each server. For exampl

Agreed. In fact, if consistent E2E encryption could be assumed, then the proxies could be implemented as simply a dedicated address on each server. For example, suppose alice@example wants to send an encrypted message to bob@server. Alice's client could wrap the message to Bob as an encrypted payload to a message addressed to switchboard@server, so that her provider doesn't learn Bob's address, and her provider could replace her metadata with switchboard@example before sending it to Bob's, so that it doesn't learn Alice's address.