I recollect that after 9/11 these “disappeared”.
On 2/12/20 I was in JFK T4 and noticed a slot in the wall near gate B30 (also near a men’s room) marked US POSTAL SERVICE, it was a small slot. Should I assume that if I deposited a letter it will be picked up by the USPS?
(Most mailboxes have pickup times noted—this one did not.)