diplomatic bag

noun

1. 外交邮袋，外交信袋（海关官员不能拆封）
   a container that is used for sending official letters and documents between a government and its representatives in another country and that cannot be opened by customs officers

1. 外交邮袋;外交信袋
   A diplomatic bag is a bag or container in which mail is sent to and from foreign embassies. Diplomatic bags are protected by law, so that they are not opened by anyone except the official or embassy they are addressed to.

in AM, use 美国英语用 diplomatic pouch

1. The diplomatic bag may contain only diplomatic papers or articles intended for official use and must be sealed and bear visible external marks of its contents.
   外交邮袋以装载外交文件或者公务用品为限，应予加封并附有可资识别的外部标记。
2. The guns were smuggled into the Embassy in the diplomatic bag.
   枪支放在外交信使袋中偷运入大使馆。
3. The diplomatic bag shall not be opened or detained.
   外交邮袋不得开拆或者扣留。
4. In so doing, it may employ all appropriate means, including diplomatic couriers or consular couriers, diplomatic bag or consular bag, and messages in code or cipher.
   通讯可以采用一切适当方法，包括外交信使或者领事信使、外交邮袋或者领事邮袋和明码、密码电信在内。
5. As a kind of "special diplomat", the diplomatic courier bears the responsibility of ensuring the confidentiality and security of the diplomatic bag.
   外交信使作为特殊的外交人员，其职责在于保证外交邮袋在传递过程中的机密和安全。