From the USPS OIG:

The Postal Service has “coupled” its retail and delivery operations, both managerially and physically, since delivery services were first established almost 150 years ago. Historical patterns, or the needs for delivery service efficiencies, primarily determined the location of physical facilities, which typically house both delivery and retail operations.

The Office of the Inspector General, Risk Analysis Research Center strategically studied the concept of “decoupling” the Postal Service’s Delivery and Retail’s physical and managerial functions. The results appear in the recently released whitepaper titled Retail and Delivery: Decoupling Could Improve Service and Lower Costs. The whitepaper drew upon the insights of key stakeholders, private sector delivery companies within the United States, foreign postal operators, and expert business consultants. The study found that selective decoupling retail and delivery, mostly outside of rural areas, could result in lower costs, increased revenue, and improved service that is more responsive to changing market conditions and customer needs that differ across the country.

Some portions of the report:

Delivery and Retail Interdependencies Are Unnecessary in the Long Term

Although co-locating retail and delivery operations in the same facility is common, their operational co-dependencies are actually few and relatively minor; rather they result largely from tradition. The major interdependency between retail and delivery operations that does exist involves shared clerk work hours. Clerks often serve both the retail window and also engage in back-office tasks such as unloading trucks and distributing mail to carriers and Post Office Boxes™. On an average day, about one third of a clerk’s work hours are used to perform “customer facing” duties, such as selling products and services at the retail window.6 The remaining hours are devoted to “back office” and administrative functions. These shared work hours seem to exist primarily to address the lack of flexibility in retail clerk hours. There is no inherent business need to have retail co-located with delivery. If reasonably increased workforce flexibility is allowed (by allowing some retail clerks to work a half day, for example), the business need for coupling could effectively disappear. The recently approved contract with the American Postal Workers Union (APWU) introduced new scheduling flexibility7 for career employees that might support this change.