Mail: - messages going from one sender to receiver(s) - works on a message by message basis - no need for a group state - no need for anyone to be the owner of the communication channel - ability to not accept replies (and communicate that!) - ability to set a price on your inbox - privacy slightly less important DMs: - needs a channel of communication (who owns it?) - privacy vaugueness Why not just spin up a Private Group for two instead, and leave the option open to get bot npubs invlved etc... ?