Originally Posted by krzysz

I am not sure if the transfer happens automatically. You need to get the "I-t-I transfer" velvet sticker attached to your baggage tag during check-in; perhaps check-in agents pay attention to it and attach it without asking, but I have always asked for it in Lima. Also, the transfer is possible if the second Int'l connection is also operated by DL; in case it is an AF or KL flight or a flight marketed by DL but operated by another carrier, you will need to recheck your bag in ATL.