Originally Posted by
suvayanr
Do this. Manually check in by clicking the check in drop down and enter your Skymiles number and the departure airport as Atlanta
This. You can check in and obtain boarding passes for up to three flights. If you have a 4th, it will simply show you a connection information document instead of a boarding pass. But checking in from the homepage and manually entering the departure city will let you check in for additional downstream segments.
So if you're flying AAA-BBB-CCC-DDD-EEE-FFF, check in once and receive BPs for AAA-BBB-CCC-DDD. Then check in again specifying DDD as your departure airport (once you are within 24 hours of that departure).