My guess is they encrypt the message twice, append it, and split it off at their servers. To anyone observing traffic, it looks like normal encrypted traffic AN

My guess is they encrypt the message twice, append it, and split it off at their servers. To anyone observing traffic, it looks like normal encrypted traffic AND they can still, if needed, show that everyone has their own key and can encrypt/decrypt their own messages. I don't think they would be brazen enough to send it to themselves in plain text.