Automated Email Message for Unused Return Labels

Currently, when a customer is issued a return label, but fails to return the package, there is no automated way to remind them to ship their item back.  We have a manual process to check return labels that have not been used after 15 days and send a manual email followup to the customer.  If they still don't return the package by 21 days, we void the return label to recoup the cost of the label. It would be great to not have to do so much of this manually.