[PhilD]

I was going to suggest making it possible to turn off item/gem sending as well as private messages, and then using anonymous TCP play, to really prevent private communications - allowing "send to all" messages for very limited coordination.

But then I remembered, it's a pretty standard thing in modern cryptography to be able to exchange private information on a public channel without prior agreement on a secret - in other words, the "sent to all" messages could be used to exchange private messages between players (all the other players could do would be to know that some player sent a private message; they wouldn't even know who it was for). So, you'd have to also take out public messages.

Still, a PBEM game with no diplomacy outside of the in-game messages would be fun - that would mean back-and-forth negociations would take two turns, so coordinating things would be a real challenge.