The US Constitution grants Congress the authority to do so if it chooses to, and historically it has chosen to. Article I, Section 8, Clause 7 of the United States Constitution, known as the Postal Clause or the Postal Power, empowers Congress "To establish Post Offices and post Roads."

More info: https://en.wikipedia.org/wiki/Postal_Clause

I do think that the US government should ensure that you should ensure that the mail continues. I just wanted to clarify that government isn't obligated to pay for it.

Where did you read this? The US postal system is not being dismantled, it’s meant to be self funded and it cannot meet its financial obligations.

> required to be funded by their Constitution.

It only empowers Congress "To establish Post Offices and post Roads." That’s the entire Post Office clause.

Since when are public services required to be self funded? Are the army, police or DMV self funded? And don't their obligations included obviously biased ( in favour of painting the post office as a financially ruinous institution and privatise/dismantle it) provisions for full pensions of future employees, which nobody else does, anywhere?