I discovered that MARTA does not have a stop at the new International Terminal (city did not want to spend the money). So, if you get off at the airport station, there is a shuttle to the International Terminal. It is easy to get to (just keep going right and when you get outside, you’ll see them on the left) and quick – 12 minutes. Once there, you can check in at the ticketing counter, go through security and get to any gate (international – E or F or domestic – A thru D). By the way, the new terminal is very nice and there is a new Crown Room upstairs after you go through security.
There & Back Again - A Traveler's Tale 