Current chat applications and email have forgotten that an address is not the same as an ID, treating the ID as the address. Emails and current chat applications send messages as [from: Alice's ID to: Bob's ID]. Regardless of how your geographical address changes, when Alice sends an email to Bob, it’s always [from: Alice's ID to: Bob's ID]. This compromises metadata privacy. 

However, letters work differently; they are [from: Alice's current geographical address to: Bob's current geographical address]. 

Keychat separates the recipient address and sender address from the ID, and the recipient and sender addresses are also different. Keychat messages are [from: Alice's one-time address to: Bob's almost one-time address]. This makes it difficult for outsiders and relay administrators to determine who is sending messages to whom. nostr:note1h842qj25shjm8yrl20y6nlm8yxynlmn33ggu2fj5mh9nmsyjnkgs8pgse4