you took a fall on that one.
6. Wrong. Secret material may be transmitted by U.S. Postal Service registered mail within and between the United States and its territories. Only Top Secret material must be transported by courier rather than through the mail.
Secret material may be sent through U.S. Postal Service registered mail through Army, Navy, or Air Force Postal Service facilities outside the United States, provided that the information does not at any time pass out of U.S. citizen control and does not pass through a foreign postal system or any foreign inspection.
Related Topics: Mailing and Carrying Classified Materials, Handling Classified Information, Marking Classified Information.