The second situation: the place where your mail is sent now needs customs inspection.
The third situation: your mail is damaged and needs to be inspected.
Legal basis: People's Republic of China (PRC) Customs Law.
Article 48 The loading, unloading, transshipment and transit of inbound and outbound postal bags shall be subject to customs supervision. Postal enterprises shall submit mail waybills to the customs. Postal enterprises shall notify the customs in advance of the opening and sealing time of international mail bags, and the customs shall send personnel to the scene for supervision and inspection on time.
Article 49 Articles sent into or out of the country by post shall be checked and released by the customs before being delivered or delivered.