Is 53 mins sufficient layover time in Atlanta?

Did you book your flights on the same ticket? If so, then your airline must think you can make it, but that's a really, really tight connection. Good news is there's a train which runs through all the domestic concourses and out to the international terminal, so it doesn't take all that long to get between them, but even the slightest delay will screw you. Also, there's a good chance of your checked bags not making it with that short of a connection, especially if there are any delays.

If your flights are on separate tickets, you will not make it, period, especially if you have checked luggage; you'll never get to the bag drop at the international terminal in time, as you'll first have to wait to pick up your luggage at the domestic bag claim, then take the slow shuttle bus to the international terminal to check it back in, and bag drops usually close 45-60 minutes before departure for international flights. Even with just a carry-on, you'll likely not manage it, and if your inbound flight is even slightly delayed (not uncommon at all at the busiest airport in the world!), you'll miss your other flight for sure. Of course, if your company is footing the bill and they're the ones who bought the tickets, then at least you won't be out of pocket for that last-minute overseas flight you'll be booking...