One way to increase the privacy of Encrypted Direct Messages ([NIP-04](https://github.com/nostr-protocol/nips/blob/master/04.md)) is for peers to derive new `one-use-only` keys when they communicate (see [NIP704](https://github.com/motorina0/nips/blob/dm-one-use-keys/704.md)).
This technique hides from the "general public" that two clients are chatting. However, the relay(s) in the middle can still see who is publishing events and who is listening for events with specific public keys.