Article I, Section 8, Clause 7:
[The Congress shall have Power . . .] To establish Post Offices and post Roads; . . .
The postal powers of Congress embrace all measures necessary to insure the safe and speedy transit and prompt delivery of the mails. 1 And not only are the mails under the protection of the National Government, they are in contemplation of law its property. This principle was recognized by the Supreme Court in 1845 in holding that wagons carrying United States mail were not subject to a state toll tax imposed for use of the Cumberland Road pursuant to a compact with the United States. 2 Half a century later it was availed of as one of the grounds on which the national executive was conceded the right to enter the national courts and demand an injunction against the authors of any widespread disorder interfering with interstate commerce and the transmission of the mails. 3
Prompted by the efforts of Northern anti-slavery elements to disseminate their propaganda in the Southern states through the mails, President Jackson, in his annual message to Congress in 1835, suggested
the propriety of passing such a law as will prohibit, under severe penalties, the circulation in the Southern States, through the mail, of incendiary publications intended to instigate the slaves to insurrection. In the Senate, John C. Calhoun resisted this recommendation, taking the position that it belonged to the States and not to Congress to determine what is and what is not calculated to disturb their security. He expressed the fear that if Congress might determine what papers were incendiary, and as such prohibit their circulation through the mail, it might also determine what were not incendiary and enforce their circulation. 4 On this point his reasoning would appear to be vindicated by such decisions as those denying the right of the states to prevent the importation of alcoholic beverages from other states. 5