 Proponents of universal service principles further claim that eliminating or reducing the PES or mailbox rule would affect the ability of the Postal Service to provide affordable universal service.If, for example, the PES and the mailbox rule were to be eliminated, and the USO maintained, then either billions of dollars in tax revenues or some other source of funding would have to be found.Some proponents of universal service principles suggest that private communications that are protected by the veil of government promote the exchange of free ideas and communications.