email notification problem

Does anyone have a suggestion on how a primary email address could be configured to be notified when a secondary email address receives a message or vice versa?

An association is planning to give its members email but most of these recepients will not check it on a regular basis and may forget about it eventually.

This association would like to automatically tickle its members primary email address’s when they have something to deliver but do not want to manage the individuals primary mailbox address changes if possible.