USPS released the following information:

On Friday, July 3, regular mail delivery services will be available. However, most Post Offices will close at 12 noon, and most collection times will be advanced to noon. Customers who may need retail or collection services after 12:00 noon on July 3 should contact their local Postmaster for information on Post Office locations that will maintain normal retail and lobby collection hours.

On Saturday, July 4, Post Offices will be closed in observance of Independence Day.
There will be no regular mail delivery on July 4. Only Sunday/Holiday Premium Express Mail will be delivered. Regular mail delivery, retail services and collections will resume on Monday, July 6.