Because I don't want the server to know "I got a message for Alice and Bob and Carol" because then it knows Alice and Bob and Carol communicate with some third party as well possibly. I want the server to know "I got a message for random one time use string A and random one time use string B and random one time use string C" because then it cannot link Alice and Bob and Carol, or one entity to another. Otherwise we could end up with a system where the server cannot tell which IP belongs to Alice and which IP belongs to Bob and which IP belongs to Carol, but it can tell that Alice and Bob and Carol communicate with each other. I want to avoid the ability of the server to tell who is communicating with who even if it cannot tie an IP address to any of the who.