The issue with the Post Office and their so-called "financial trouble" is the work of Bush-era Republicans in Congress wishing to privatize the postal service and at the same time do away with the largest public employees union in the country. While it is true that how mail and packages are being delivered in this country has had some big changes, but if it weren't for the fact that they are being forced to PRE-FUND, over a period of 10 years, the pensions and retiree healthcare costs for employees, some of whom have not even been born yet, out 75 years from the day the law was enacted. No other organization, private or public, is being forced to pre-fund their pensions and retiree healthcare of all future employees out 75 years. If you did that to say GE or AT&T or for that matter, the military services, they would be in financial trouble as well, but NO, ONLY the Post Office has been burdened with this requirement. And it's being done this way so as to force the insolvency of the Post Office since it can't actually be privatized for any other reason since it's the ONLY agency that was founded as the result of a Constitutional provision.
For some insight into this issue, go to:
http://deliveringforamerica.com/resources/PreFundingFactSheet_final.pdf
http://www.nalc.org/government-affairs/body/2015-pre-funding-fact-sheet.pdf
http://www.uspsoig.gov/blog/be-careful-what-you-assume