When the onset of the American Civil War ended postal service between the North and South, express companies such as Southern Express Company carried mail, primarily civilian business mail, across the lines. The U.S. Post Office Department ordered an end to such traffic, effective August 26, 1861. Thereafter, mail had to be sent by Flag-of-Truce. The U.S. imposed special regulations to control, inhibit, and delay civilian through-the-lines mail and letters to prisoners on the other side. The same inner and outer envelope requirements were mandated that applied to prisoner mail. Mail could only cross the lines at specified exchange points. Mail going from the North to the South passed primarily at City Point, Virginia; mail going from the South to the North passed primarily at Fortress Monroe, Virginia.