DDP packages marked as Returned to Sender rarely make it back to the United States due to foreign postal service and customs requirements. In these cases, it will most likely have been sent to an abandonment center to be destroyed. Most often, it's also cost-prohibitive to have the item returned from the abandonment facility to the United States as there is often a retrieval fee, the cost of shipping via FedEx back to the U.S., customs duties levied by U.S. Customs upon re-entry, etc.
DDU packages marked as Returned to Sender DO often make it back to the United States, as they are shipped through the postal system. The United States Postal Service (USPS) has reciprocity agreements with many other countries' postal systems and will most likely be able to get the shipment returned.
In the event that we do receive a shipment back in our processing facility, we will ship these packages back to our brand partner warehouses/3PLs on a quarterly basis.