I took a mailbox full, just 2 days of mail, 99% spam, and took it into my local post office. Plopped the mail on the counter and told the clerk I no longer wanted to receive mail from any of these advertisers.
Of course the clerk couldn't help me. USPS makes too much money delivering junk right to your mailbox. What a great system we're engineered here, where our national carrier service primarily slups junk mail around the country, and won't stop because it's one of their most profitable side-hustles.
https://faq.usps.com/s/article/Refuse-unwanted-mail-and-remo...
So quite a lot.
Besides the fact that this isn't true (you'd be astonished at the number of homes that USPS won't deliver to, generally rural areas[1]), it doesn't preclude USPS from being profitable if managed properly.
Let's not pretend if USPS could ditch some routes it would suddenly be profitable and not need billions of tax payer capitol injection all the time. They're a long ways from that.
Saddled with thousands of unproductive employees, ones that will never be fired, yet collect a paycheck paid for by tax payers, and will enjoy a comfortable retirement with all that pension money. USPS might be a quasi-private company, but they sure don't behave like a private company.
[1] I'm in the industry. For these shipments we have to send them FedEx or UPS, whichever is cheapest usually, since both will deliver when USPS will not.