挂号信的英文：
certificate mail

参考例句：

I signed for a registered letter.
我签收了一封挂号信。

This time it was the postman and he wanted me to sign for a registered letter!
这次是邮递员让我签收一封挂号信！

There is twelve registered letters to be sent in addition to this packet.
除了这个包裹外，还有22个挂号信也需投寄。

certificate是什么意思：
n. 证明书；执照；凭证，单据；证券；纸币
v. 发证书给；用证书批准；用证书证明

gold certificate
金币流通券|金券|金证券

scrap certificate
车辆拆毁证明书

A certificated lawyer.
合格的律师。

The certificate revocation list for this certificate authority that issued this site's certificate has expired.
发出此网站证书的证书权威的证书撤消列表已过期。

Here is the certificate for this Certificate Authority. Examine it carefully.
这里是此

mail是什么意思：
n. 邮政，邮递；邮件；盔甲
v. 邮寄；给…穿盔甲

Send the memo by express mail.
把这份备忘录用快递寄出。

mail and luggage van
邮政行李车

This parcel came in the mail today.
这个包裹是今天邮来的。

Cn you please confirm that you have received this mail.
您能否确认已收到此邮件

The mail was delivered late today.
今天邮件送得迟了。