airports – Can I check-in and clear security at the international terminal in Atlanta for a domestic flight?

Yes. The TSA does not care what terminal you use, and the documentation requirements do not change in any way. You are entering the same sterile area no matter which checkpoint you go through. The international terminal is the site of a pilot program using CT scanners instead of traditional X-ray machines, so who knows if that will speed things up or slow them down. The upside is that electronics no longer have to be removed from bags.

In some cases, if you need services at the checkin desk, that may be an issue as some airlines either do not have a desk in the international building or do not provide services to domestic passengers there. Just to be safe, I would be sure to get my boarding pass printed in advance or on my phone. If you have to check a bag, I would definitely call ahead and make sure.

The airport would rather you not do this, as it messes up predictive staffing, but that’s their problem not yours. No rule against it.

By the way, the reverse of applies if you have an international flight going out of ATL and want to take MARTA or park in the domestic garages and avoid the long bus between terminals. The only thing you can’t easily due is get back from an arriving international flight to the domestic terminal if you have to check bags because you won’t be able to re-enter the secure area to take the train, so you’ll have to take the bus.