On an early spring morning in 1849, an enslaved Black man named Henry Brown folded himself into a three-foot by two-foot wooden crate. Twenty-seven hours and 350 miles later, he arrived at the home of William Johnson, a Philadelphia barber who collaborated with the Underground Railroad, a network of people, safe houses, and routes that guided enslaved people to freedom.

The American postal service was on its way to becoming an advanced information highway, and abolitionists had quickly grasped its potential. As they flooded southern states with anti-slavery writings, those in favor burned bags of mail and postmasters picked out abolitionist materials. The fledgling postal service was thrust into the center of a national argument about free speech, censorship,