The Street--Amazon.Com (AMZN_) announced it will start delivering packages on Sunday, through the U.S. Postal Service.

The service starts this holiday season in New York and California. It's due to expand into other markets next year.

But wait, you say. Isn't the Postal Service killing Saturday delivery? They planned to do that starting last August. Congress stopped them. Yet now they're adding Sunday operations, for Amazon packages. Something doesn't add up. Read more!