When the Civil War forced an end to postal service between the North and South, express companies carried mail across the lines for nearly two months. They carried primarily civilian business letters. 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 as applied to prison mail were mandated for all mail. Mail could only cross the lines at specified exchange points. North-South mail passed through City Point, Virginia, and South-North mail passed through Fortress Monroe, Virginia.