Do you have one ticket or two? When do you fly? Delta recently changed their rules which take effect sometime next year whereby they wont through check luggage if you have a separate ticket for the connecting flight.
On the return trip the originating airline should follow the "most significant carrier" rule and give you the same luggage allowance as Delta and should check the luggage through.
It's all booked through a single itinerary on Delta, so it's all strung together. And thanks. Is my best option to just say that I'm connecting to an international flight, and here's my baggage allowance for that flight?