Postal Service Electric Fleet Authorization Act of 2021 This bill establishes requirements for U.S. Postal Service (USPS) acquisition of vehicles and the infrastructure required to operate a fleet of electric vehicles. The bill's provisions only apply if specified funding is appropriated. Specifically, the bill requires the USPS to ensure that at least 75% of the total number of next generation delivery vehicles purchased using such funds are electric or zero-emission vehicles. The bill provides for a phase-out of medium- and heavy-duty vehicles that are not electric or zero-emission vehicles. The USPS must provide by January 1, 2026, at each postal facility accessible to the public, at least one electric vehicle charging station for use by the public or USPS officers and employees.