Firstly, since 1971 the Postal Service has operated independently, receiving no taxpayer money (other than about $100 million allocated by Congress to offset the cost of providing free mailing for blind people, overseas mailing, etc).

Until 2006, the Postal Service was entirely self sufficient, with no debt and no need for taxpayer funding.

However, in 2006 Congress passed a law requiring the Postal Service to prefund future retiree's health benefits (75 years in advance), which costs $5.6 billion per year. By 2012, the Postal Service hit its $15 billion debt limit, directly because of this.

The Postal Service itself does not lose money, and does not require funding, because it sells postage-- mailing is not free. The insane policy that Congress has foisted on it does lose taxpayer money, by requiring it to do something as far as I know no other organization does or is required to do.

If you want to fix the budget deficit at the Post Office, simply get that law repealed.