United States Postal Service 407 E Main St, Port Jefferson, NY11777 This branch of the United States Postal Service is located in a historic building in downtown Port Jefferson. …More There are drop-off mail boxes outside the building. The last daily pickup at this location is 4:30pm, and 1pm on Saturdays. PO boxes can be applied for and managed online. Visit the USPS website for full information and services including stamp purchase, postage calculation, mail tracking, printing shipping labels and forwarding or temporarily stopping your mail. For TTY Service for the hearing impaired, call 877-889-2457.