USPS gets into the SPAM business
usps.com
usps.com
Prepaid is the only way to do pensions.
If you don't pay pension obligations as you incur them, you're going to run into trouble if there's any biz contraction. And, if it's a long-lived organization, you don't actually reduce your cash-outflow by not paying when you incur.
Run a scenario where you under pay by X%. When folks start collecting, you have to come up with the difference out of then-current revenues. Steady-state with stable revenues, you end up paying exactly the same amount, but you've got debt. Now cut the revenue (and current expenses) by 25% because the world changed. Your revenue can't pay the debt.
How do we finance social security again?
Companies seeking such a service typically resort to purchasing homeowner information in bulk from other services. With such a USPS service, it decreases the demand for such databases, and with it the incentive to create such databases.
It is unlikely that the USPS will overwhelm homeowners. Presumably the USPS will limit received promotions to one per day. That can potentially give the USPS an additional $60/year in revenue per household, at marginal cost.
Mail Preference Service deals with addressed mail.
Royal Mail deals with "Door to Door" unaddressed mail delivered by Royal Mail.
Nothing stops people just shoving junk mail through your door.
Another thing I'd suggest is https://donotcall.gov/. Registering there seems to have had a positive impact on the number of spam calls I receive.
It should be a very effective marketing tool for local businesses and it helps the USPS stay in business. If they would just add opt-out there would be nothing to complain about IMHO.