Yes prisoners of war on both sides were allowed to send and receive letters to or from home weather that be either the Confederate States or the United States.It is a fascinating subject and to the prisoners of great personal importance second only perhaps to surviving and getting something to eat.

In the case of Andersonville/Camp Sumter,there was a mail box located within the stockade.A CS stamp would get the letter thru the Confederacy to Old Point Comfort and a US stamp or postage due notation would take it from there.All outgoing letters would be marked Prisoner of War with the notation HW(examined by Henry Wirz).It is interesting,the Confederate States government furnished their prisoners in the north free CS postage stamps.The United States government did not.