Would take way more than one letter to make USPS profitable.
Their core business has been declining for the past 20 years and business mailer lobbyists work very hard to keep the current price caps. This idea that we should let the finances spin out of control and raise taxes is entirely new idea.
Standard communication (including addressing) is such a basic, critical function of government that it only makes sense to do it at scale and just fund it with taxes.
Your approach leads to exploding federal budgets, which are already the bane of the US, Canada, and the EU. When will you learn? Everything is not the exception, everything is the problem.
When will you learn? Taxes are not “the bane” of the EU, taxes are why It’s a nice place to live and America isn’t.
New developments incur impact fees to offset their immediate effects on the roads, sewers, and sidewalks. Police charge a fee to connect your alarm system to their dispatchers, an hourly wage for an off-duty cop to stand guard at your commercial premise, and a fine if you waste their time with false alarms. Fire services tend to send you a bill for a false alarm, a fee for an inspection and, if you did it on purpose, a criminal charge plus the full cost of the response. And lord forbid you accept EMS services…
All are tax-funded, but all gesture at apportioning costs proportionally to use. If they send this much junk mail while it’s quarters-a-pop, how much would they send if it were free…
(It's also not a surprise that the Congressional mandate to run the USPS as a for-profit has been used as much to make the USPS profits a slush fund of "free money" that Congress can use for non-USPS projects, including pork barrel projects. The for-profit mandate isn't just for threatening the shutdown of USPS services.)