When a letter is sent to an address it is immeditately put into the delivery schedule for the day when it arrives at the local depot.
This means that post(people) deliver the post every day and to every address (i.e. you can recieve a letter on monday and a letter on tuesday)
The solution is to only deliver a postcard which is like a mail notification (the postcard will say; i.e. you have 10 letters)
This way when the post office is storing those letters for more than 3 months or so they would know to notify the sender that someone is not responding to the letters. This would reduce junk mail and also remove the need for multiple deliveries in the same week to the same address.
This is also the perfect solution for delivery of bulky items, on a majority of occasions items are sent to an address when noone is there to collect (they have jobs) instead of this the person expecting a package on the said day can just go directly to the post office to collect that item.
An addition to this solution is to combine train stations and post offices, the postal service will then be able to use the trains as part of their delivery network and further save on fuel costs; the main benefit is that the delivery staff that would have lost jobs by no longer daily delivering would use their resources to shuttle the mail from one post office to another.
This would be a definitive solution to solve the debt in the postal service.