The code APO AE on a package or letter indicates that it is to be delivered to a recipient at a US Army post office routed through Europe. This may indicate that the recipient is stationed in Europe, or somewhere in the Middle East.
There are a total of six military and diplomatic codes used to send mail overseas. APO indicates an Army recipient, while FPO indicates a fleet post office. DPO is used for diplomatic recipients. AA following the three-letter code indicates that the package is destined for somewhere in the Americas, while AE indicates Europe and AP indicates a Pacific or Asian destination.