The postal service is a public service, and if we have to run it at a loss for a while that’s fine. Nobody expects the road system or the military to pay for itself.
It's like asking if a family can live on $50k a year but then stipulating that oh by the way in this family the father gambles 90% of his earnings away at the casino on payday. It doesn't really answer the question.
[0] https://www.pbs.org/wnet/need-to-know/five-things/the-u-s-po...
They don't. Junk mail subsidizes everything else USPS delivers, and USPS is entirely self-funded.