Originally Posted by beachmouse

Border exit control in US airports is entirely behind the scenes- after your flight leaves US air space, the airline transmits an electronic passenger and crew manifest with passport info to CBP and you are ‘checked out’ of the country.

Moat US airports simply can’t justify a sterile transit/international concourse so no one has those and the same gate that gets used for International arrivals from Jamaica is also the domestic gate to Grand Rapids once the cattle fencing directing international arrivals through immigration is reset for a domestic departure