On the seventh day, the U.S. Postal Service (USPS) delivered. And it may be interested in doing a lot more of it.

The USPS announced earlier today that it had begun limited Sunday deliveries of parcels from e-tailer Amazon.com. A USPS spokeswoman also said today that the organization would be willing to discuss the idea with other interested shippers.

The Amazon service, which began yesterday in New York and Los Angeles, calls for the Seattle-based company to bring parcels to local post offices on Sunday mornings for deliveries later that day. The service will be expanded next year to a "large portion of the U.S. population," Amazon said in a statement. Markets mentioned in the statement were Dallas, Houston, and New Orleans.

The service is available to those who've signed up for "Amazon Prime," which provides free unlimited two-day deliveries for a $79 annual fee.

Sue Brennan, the USPS spokeswoman, said if other merchants are interested in Sunday deliveries, "we'd be happy to talk to them." The new Amazon relationship is a contractual agreement, however, and does not signal the launch of a concerted marketing campaign, she said. USPS already moves parcels for Amazon under its traditional arrangement.

The Sunday service with Amazon does not call for USPS pick-ups, nor does it involve the USPS' infrastructure beyond what's required to deliver from post office to destination. USPS historically delivers packages on the two or three Sundays leading up to Christmas in major metro areas, Brennan said.

Rob Martinez, president and CEO of Shipware LLC, a San Diego-based parcel consultancy, said that like the push for same-day delivery services before it, Sunday deliveries "may be one of the greatest things the market isn't asking for." Although he likes both concepts, Martinez said that, "we just haven't seen significant market adoption of the former, and I don't expect it of the latter."

However, Martinez offered the caveat that Sunday deliveries could become the "new normal" in the years ahead as time-pressed consumers prefer to receive packages after hours and on weekends when they are more apt to be home to receive them.

"If I complete an online transaction on a Friday, and I'm offered Monday delivery or upgrade to Saturday or Sunday delivery at no additional charge, I'd opt for the weekend delivery," he said. "But I wouldn't pay more for that service" unless it was to meet a very urgent need.