Time is running out to send packages to overseas military in time for Christmas. The U.S. Postal Service said priority and first-class mail must be shipped by Friday. Expedited mailing services are offered until Dec. 16. The Postal Service offers its largest priority mail box at $16.75, which includes a $2 per box discount for mail destined for APO/FPO/DPO. For information about packing, addressing, and shipping items to U.S.