If you're departing from the international terminal, you can either check in from the domestic terminal (if your airline allows), or take the free shuttle to the international terminal.
Atlanta has a domestic and international terminal with concourses A to F and T. To help you make your connection, once you arrive you will need to clear immigration, collect your bags, check in with the next airline, clear security and head back to the departure area.
It varies. They will often wait a little while, especially if it's the last flight of the day and even moreso if there are multiple passengers making the same connection. I've had Delta wait for me after inbound connection delays on several occasions.
Domestic flight - international flight: 40 minutesExceptions: If your inbound flight is on a 330 or 767, then the minimum connection time is 50 minutes for a domestic-international connection. The minimum domestic-YYC connection time is 45 minutes. The minimum domestic-HAV connection time is 55 minutes.
Overall, passengers usually have to re-clear security for connecting flights, though there may be some exceptions depending on the airport and flight itinerary. To make this process easier, checking with the airline or airport ahead of time is recommended.
7) CONNECTING FLIGHTS. After exiting security, you're free to proceed to the gate for your connecting flight. If traffic is not high, this process usually takes about 30-45 minutes (less if you didn't check bags), but it can take longer at peak times and if you are not a citizen/resident.
Everyone's individual levels of comfort are different, but I'll just say this: my ideal layover time in Atlanta is 1 hour and 10 minutes for domestic flights, and 2 and a half hours for international flights. This amount of time allows two things: First, it allows me to walk at a leisurely pace to my connecting flight.
If you checked a bag, you'll have to collect it from baggage claim from the international flight. You'll need to clear customs and immigration. Next, you'll recheck your luggage for the domestic flight.