My prescription for long-term solvency:
1. Sell excess facilities
2. Bust the union
3. Reduce excessive pension costs
4. 3-day-per-week mail delivery (MWF, TTS) (thus eliminating 50% of the carriers)
5. Eliminate ludicrously inefficient walking routes (mandate curbside mailbox gangs), thus eliminating more carriers by enabling many to deliver more mail (maybe the USPS hasn't noticed, but the automobile was invented about 110 years after the Postal Service's founding, and now they even make funny little trucks!)
I'd offer my services as Postmaster General, but I'm busy running my own business with increasing efficiency; besides, I vowed forty years ago never again to work for a government.
One minor step they could take is to raise the rates on junk mail.
Dealing with the union and with gross inefficiencies in some of the larger POs is more important, but also more difficult.