该功能可以让收件人以发件人同样的方法，在不产生任何费用的情况下，用回件方式退出收件人名单。

This facility must allow the recipient to unsubscribe by sending a message back to the sender, using the same method used by the sender without incurring any costs.

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若已产生任何费用和利息，卖方有权先将该付款当作支付费用，然后为利息，最后再当作主债权的支付。

If costs and interest have already accrued, the Seller is entitled to count the payment towards the costs first, then towards interest, and finally towards the principal claim.

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有人说，口碑营销是一种最便宜最有效的营销，因为口碑传播者通常都是自觉传播的，传播过程中不产生任何费用。

Some say a word-of-mouth marketing is the cheapest most effective marketing and word-of-mouth as communicators are usually conscious of the spread, and spread the process does not produce any cost.

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