There are two counter-arguments to that:

1) UPS is not allowed to deliver first class mail to a letterbox, or at the same cost as USPS.

2) Why should short-distance mail subsidize long-distance mail?

> UPS is not allowed to deliver first class mail to a letterbox,

So? They regularly leave packages on your porch, they'd do the same for letters.

> or at the same cost as USPS.

Which is insanely low and money-losing in many cases. And first-class mail is a declining business. Do they even want that?

I was responding to a comment that said: "The day that UPS will be obligated to deliver a first-class letter... for 55 cents". UPS is legally required to charge at least six times more, and cannot use letterboxes.[1] The use of letterboxes is a cost-savings; if it were not a competitive advantage, the USPS wouldn't need a law protecting it.

Whether or not UPS wants the business is beside the point, and they currently cannot have it.

[1] https://www.law.cornell.edu/uscode/text/39/601

> Whether or not UPS wants the business is beside the point, and they currently cannot have it.

It's the entire point actually.

The key part of my post is:

> The day that UPS will be obligated... to deliver a letter for 55 cents

The USPS is forced to provide this service - at a ridiculously low price. The second that UPS and Fedex have to play by the same rules (By being forced to deliver negative-margin mail), they will stop being profitable.

The letterbox might have been a competitive advantage when people weren't accustomed to having stuff delivered to their porch. Not anymore. Ditto for a first-class mail monopoly - advantageous when people actually wrote letters, practically useless today.

Letterbox delivery is a competitive advantage because it saves money on delivery; the driver can often drop letters off in a mail room at a multi-unit dwelling, or by the road in the suburbs/rural areas.

We're only talking about first-class mail here, so a 6x cost advantage in first-class mail is very important.