Flawed reasoning. The customers of the Post Office are those who pay the postage,not those who receive the letters. These two would have done better going after the revenue side.
If the senders of all that junk mail would be forced to pay not only the postage of what they sent, but also the cost of having it all sent back to them, not only would the demands on the USPS be reduced dramatically but their overall operating costs and employee efforts would be diminished by a considerable factor. Then perhaps they would not be operating under a continual financial black hole year after year.