When postal service between the North and South ended at the onset of the Civil War, express companies carried mail across the lines. This continued for nearly two months before 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, although express companies continued to do some illegal business. To send a piece of correspondence by express carrier, a sealed and addressed letter with fifteen cents to twenty-five cents was enclosed in a second envelope. This package was sent to the nearest express office for forwarding. Part of this amount paid for the postage, and the balance was the company's fee. The major express companies were Adams Express, American Letter Express, and Whiteside's Express.