Their Amenities and Services page lists a USPS collection box in the airport’s “cell phone lot”.
I wasn’t able to confirm this using Google Maps, and that seems to be a strange place to put one. There is a building next to the cell phone lot, so it’s certainly plausible there’s a collection point there.
Robert notes that there is a blue mailbox curbside across from ticket counters.
Google Maps shows this pretty well; it looks like the nearest door is closest to the Delta ticket counters.
Collection time is Monday-Friday at 10am, Saturday at 10:30am.
Last Updated 23 November 2021