That’s the Post Office’s goal. Doesn’t seem like they have a viable plan for that, though.

Postmaster General Louis DeJoy is preparing to put all first-class mail onto a single delivery track, according to two people briefed on his strategic plan for the US Postal Service, a move that would mean slower and more costly delivery for both consumers and commercial mailers.
[They plan to] eliminate a tier of first-class mail—letters, bills and other envelope-sized correspondence sent to a local address—designated for delivery in two days. Instead, all first-class mail would be lumped into the same three- to five-day window, the current benchmark for nonlocal mail.

And

The plan also prevents first-class mail from being shipped by airplane….

After all,

The Postal Service spent more than $457 million flying first-class mail in 2020, according to data it filed with the Postal Regulatory Commission, and spent $314 million transporting mail by truck.

Of course, putting all that air cargo onto trucks won’t increase truck transport cost. Uh, uh.

Oh, and the Post Office is planning to raise postage rates in order to make up for this degradation of service.

Brilliant.