The USPS does make a profit; however, they are required by law to pay for the health care of future employees that aren't on the payroll yet.
http://www.govtrack.us/congress/bills/109/hr6407
Section 803 -
Transfers responsibility for paying the government's contribution of the health benefits of postal annuitants, effective in FY2017, from the Postal Service to the Postal Service Retiree Health Benefits Fund (established by this section) up to the amount contained in the Fund, with any remaining amount to be paid by the United States Postal Service. Establishes in the Treasury the Postal Service Retiree Health Benefits Fund, to be administered by OPM. Requires the Postal Service, beginning in 2007, to compute the net present value of the future payments required and attributable to the service of Postal Service employees during the most recently ended fiscal year, along with a schedule if annual installments which provides for the liquidation of any liability or surplus by 2056. Directs the Postal Service, for each year, to pay into the above Fund such net present value and the annual installment due under the amortization schedule. Makes OPM actuarial computations subject to PRC review.
http://www.gpo.gov/fdsys/pkg/USCODE-2010-title5/html/USCODE-2010-title5-partIII-subpartG-chap89-sec8909a.htm
(B) Not later than June 30, 2017, the Office shall compute, and by June 30 of each succeeding year shall recompute, a schedule including a series of annual installments which provide for the liquidation of any liability or surplus by September 30, 2056, or within 15 years, whichever is later, of the net present value determined under subparagraph (A), including interest at the rate used in that computation.
(3)(A) The United States Postal Service shall pay into such Fund—
(i) $5,400,000,000, not later than September 30, 2007;
(ii) $5,600,000,000, not later than September 30, 2008;
(iii) $1,400,000,000, not later than September 30, 2009;
(iv) $5,500,000,000, not later than September 30, 2010;
(v) $5,500,000,000, not later than September 30, 2011;
(vi) $5,600,000,000, not later than September 30, 2012;
(vii) $5,600,000,000, not later than September 30, 2013;
(viii) $5,700,000,000, not later than September 30, 2014;
(ix) $5,700,000,000, not later than September 30, 2015; and
(x) $5,800,000,000, not later than September 30, 2016.
Billions of dollars vs. $50,000. Yes, the salary of a janitor is the problem..