From the USPS Office Of Inspector General’s Blog:
Although eliminating Saturday delivery has been heavily debated, reducing delivery to 5 days a week may not be enough. There has been some discussion of whether the viable model for the U.S. Postal Service of the future will incorporate 3-day delivery.
A 2010 study by the Boston Consulting Group for the Postal Service forecasts that the average pieces of mail per delivery point per delivery day will drop from 3.8 to 2.8 by 2020. If this projection holds true, then more household will likely receive no mail on any given day. With the increasing availability of alternative communication choices, it is unlikely that the demand for mail delivery will ever return to previous levels. Therefore, postal delivery may only be needed 3 days a week. Some homes could receive mail on Monday, Wednesday, and Friday, while others, on Tuesday, Thursday, and Saturday.