He asked his mother to send it by registered mail.

他让他妈妈用挂号邮件寄。

How much is it by registered mail?

挂号邮寄要多少钱？

Can I send this by registered mail?

我可以用挂号寄这封信吗？

How much is the by registered mail?

挂号邮寄要多少钱？

Please send this by registered mail.

请用挂号邮件寄这个东西。