/msg doesn't even give a fuck on who'd you like to get messages from.
He is talking about just seeing all PMs sent in his server.
Well, I suggest you to leave players send PRIVATE messages, and if someone will be annoyed, then he will report that to an admin.
By the way, to ad everybody using pms, the player should do something like that:
/msg 0 COME TO MY NEW SERVER COOL BEST. IP: 0.0.0.0:0
/msg 1 COME TO MY NEW SERVER COOL BEST. IP: 0.0.0.0:0
/msg ....
Will be needed to retype the whole message for every player apart, because you can't just jump to the first parameter, and edit it, without removing what's next, and that's not entertaining.