Answer:
Abolitionism was outlawed in the South and it was not possible to send abolitionist publications, such as the Liberator to the South by post. Postmasters would manually remove all the abolitionist mail, while possession of abolitionist publications could lead to being publicly whipped.
South was outraged and terrified with the ideas of abolitionism and tried to keep them out for as long as was possible, though, of course, ideas do not circulate only in printed form.
