Which item is explicitly prohibited from being used for the transmission of classified information?

The option that specifies the use of the U.S. Postal Service for the transmission of classified information is explicitly prohibited due to the inherent risks involved in using a public mailing system. While the U.S. Postal Service can facilitate the delivery of many types of materials and packages, it does not provide the necessary security measures required for handling classified information. This includes the potential for interception or unauthorized access, which poses a significant risk to national security.

In contrast, designated cleared couriers and military couriers are specifically trained and authorized to transport classified materials securely and are subject to stringent protocols to safeguard that information. Similarly, the use of electronic means involving encryption is an acceptable method for transmitting classified information, provided that appropriate security standards and encryption techniques are employed to protect the data during transmission. Therefore, the prohibition of the U.S. Postal Service for classified transmissions reflects the need for secure and controlled methods in handling sensitive information.