I don't care what technology you want to use, saying that you want to send something out to some people and not have it get to other people doesn't work
This is especially bad if you don't want to tell the people you are sending it to that you don't want the third person to see it as they have no reason _not_ to forward it, or quote it to that person
as for inbound messages, your system should accept them and then delete them. Yes it eats bandwidth, but it is both simple and reliable.