How's the Post Office doing financially?

Terribly. For the past 11 years it has incurred large operating losses that it expects will continue. Furthermore, it claims that its opportunities for revenue generation and cost-cutting are limited. 

I learned this by looking at the GAO report on the status of the Postal Retiree Health Benefits. The report shows that at the end of fiscal year 2017, the fund’s assets declined to $49.8 billion and unfunded liabilities rose to $62.2 billion. It is estimated that the fund will reach $0 by fiscal year 2030 if the Postal Service continues to make no payments into the fund.