Amazon strikes again. In a deal with the beleaguered U.S. Postal Service, customers in the Los Angeles and New York metropolitan areas will be able to have packages delivered on Sunday at no extra charge. The deal is a major boon for Amazon, as other delivery companies don’t really deliver on Sundays. UPS doesn’t deliver on Sunday at all, and FedEx has limited and expensive options to do so. The U.S. Postal Service may look at the deal with Amazon as a way to grow the one strong part of its business—packages. Amazon plans to expand the deal to Dallas, New Orleans, and other cities next year.