If I am shipping my package to an APO/FPO, do I have to pay international or domestic shipping rates?

I am shipping a product that I sold on eBay, but the person that bought it is at Camp Liberty, Iraq. Does that mean I have to pay full international rates for shipping through USPS (United States Postal Service), or do I pay Domestic Flat rate which is like $10.50 compared to international flat rate which is $45.50.

So basically which one, international to Iraq or Domestic flat rate?