Related to this is a common corporate problem where someone has a problem they perceive as somewhat urgent. They often send a message to several people, hoping to get the first possible answer. Sometimes the recipients experience diffusion of responsibility and no one answers, because each believes someone else is better able (or less busy).

There are systems with retraction capabilities for senders (e.g. Bloomberg MSG, though it is no competitor on price). But I haven't seen anything like a system which would downgrade messages already seen by others, etc.