名词短语
中文翻译：邮资不足的信件
同义词：
['unpaid post', 'insufficient postage', "overdue mail例句：1. The company's policy is to send unpaid postage for international orders.（该公司的政策是对于国际订单收取未付邮资。）"]
例句：
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1. The company's policy is to send unpaid postage for international orders.
该公司的政策是对于国际订单收取未付邮资。
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2.The sender was unaware that the postage was insufficient.
发件人不知道邮资不足。
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3. The overdue mail has been returned to sender.
逾期邮件已被退回给发件人。