United States Postal Service 6411 Baltimore Ave, Riverdale, MD20737 This post office is a stand-alone brick building. This location offers express and priority mail and international…More shipping, but not passport services. It does, however, take faxed stamp orders so customers can just stop by and collect their purchase. There are two mailboxes outside. Collection times at those mailboxes are 10am and 3pm on weekdays and at 1pm Saturdays.