Regulations Governing the Handling of Mail Article 54

“Postage due mail” refers to a mail item for which postage was not paid or was insufficient.Unless otherwise stipulated, the postage due and accrued postage due charge shall be collected from the addressee.
中文原文 郵件處理規則第54條
未付資費或未付足資費之郵件,為欠資郵件。
欠資郵件,除另有規定外,向收件人收取欠資及欠資手續費。

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