I come from a postal family: two of my aunts, one of my godfathers, and a slew of family friends are employed by the Postal Service; my mother has been a rural letter carrier for more than thirty years. She’s driven tens of thousands of miles along the same stretch of roads, tracing the same route almost every day for decades. She’s delivered everything from gold bars to live bees, diamonds, turkeys, tombstones, crickets, ducks, pheasants, and human ashes.

I remember watching my mother’s careful hands sort the mail for customers on her route, listening as my aunt assisted clients at the clerk’s window, and studying the conveyer belts full of packages and envelopes as machines read Zip Codes while my godfather supervised the local processing plant. That any envelope or scrap of paper found its way from one coast of the country to the other struck me as a miracle when I was a child; frankly, it still does.

It’s rare to hear anything but complaints about mail being lost or carriers being discourteous, but the mail is one of those things to which we give distorted attention. Almost every day, it arrives without error or fanfare. Yet on those days when it doesn’t, we notice.

Only nine months after announcing that it planned to reduce regular delivery from six to five days a week, the United States Postal Service revealed earlier this week that it would be delivering packages on Sundays for Amazon.com. Starting this Sunday, if you live in Los Angeles or New York, your postal carrier could be knocking on your door with an Amazon package.

The negotiated service agreement between Amazon and the U.S.P.S. is sealed, but representatives and press releases from both companies explained the unusual arrangement. Postmaster General Patrick R. Donahoe told the Times, “Consumers have shown that there is a market for package deliveries seven days a week, and we are glad to be in a position to partner with Amazon on providing this service.” Dave Clark, Amazon’s vice president of worldwide operations and customer service, said, “We’re excited that now every day is an Amazon delivery day.”

While the Postal Service already delivers some express-mail packages on Sundays for an additional fee, the agreement with Amazon greatly expands Sunday delivery. It’s not clear who is covering the additional cost for weekend service. Millions of products qualify, although only the Los Angeles and New York metropolitan areas are eligible for now. As early as next year, the same service will be available in Dallas, Houston, New Orleans, and Phoenix.

It’s a win for all involved: consumers, desperate for last-minute deliveries during the holiday season; Amazon, eager to stay ahead of its online competitors; and the U.S.P.S., which continues to lose money on regular mail but hopes to grow its package services. While first-class-mail delivery fell from ninety-two billion pieces in 2007 to sixty-nine billion in 2012, package volume rose from 3.3 billion to 3.5 billion in the same period.

The Postal Service’s effort to stay profitable is hampered by its unusual status as independent government agency. While U.S.P.S. hasn’t received government funds directly for decades (funding comes entirely from postage and product revenues), the agency is still subject to special regulation by Congress. There is very little the Postal Service can do without congressional approval: for example, consider Congress’s prerogative to name post offices.

Likewise, almost no element of the Postal Service’s plan for profitability can be implemented without congressional approval. Among the reforms that require it are ending Saturday mail delivery, consolidating rural offices and regional sorting facilities, restructuring employee benefits, even raising stamp prices by a single penny. Annual revenue fell by half a billion dollars last year, and while cutting Saturday delivery alone would save two billion dollars, Congress has opposed any such reductions in service.

That’s one of the reasons the agreement with Amazon.com is so notable: it represents the U.S.P.S. acting within its limited power to become more profitable. Perhaps it is the first of many such arrangements that the Postal Service will make with online retailers, hoping to capture the delivery market for these sites instead of other carriers like FedEx and United Parcel Service. Even while other countries are privatizing their mail services, the Postal Service has asked for reform, not privatization.

U.S.P.S. handles forty per cent of the world’s mail—that’s more than a hundred and sixty billion pieces annually. The inscription carved above the entrance to the James A. Farley Post Office Building on New York’s Eighth Avenue turns out to be more often true than false: **“**Neither snow nor rain nor heat nor gloom of night stays these couriers from the swift completion of their appointed rounds.” Now we can add funding troubles to the list of deterrents that will not stop the U.S.P.S., if it has its way.

Photograph by Andrew Harrer/Getty.