Postal Act Article 32

When a mail item is delivered to the addressee or returned to the sender, it shall not be deemed damaged should there neither be loss of weight nor visible surface damage. Nor shall it be considered damaged when the weight reduction is due to the nature of the contents of the mail item.When a mail item is delivered to the addressee or returned to the sender, should it have lost part or all of its value due to the lapse of time or market fluctuations, it shall not be deemed to have suffered any losses.
中文原文 郵政法第32條
郵件遞交收件人或退還寄件人時,如封面無破裂痕跡,重量亦未減少者,不得以毀損論。
重量雖減少,其原因由於該物件之性質者,亦同。
郵件遞交收件人或退還寄件人時,如因時間關係或市價變動而減損其全部或一部價值者,不得以損失論。

English translation for reference only; the Chinese text prevails. Not legal advice.