Certified mail protocol is fair exchange of a message m for a receipt.

认证邮件协议，指一个发送方要将消息M与收方收到的证据进行交换的协议。

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For many organizations, the need for a mail protocol is only part of the problem. They also need a way to share.

对于许多组织而言，对一个电子邮件协议的需求只是这个问题的一部分。

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MIME is an extension of the E-mail protocol, to allow other types of data to be exchanged over the Internet, such as video, images, and applications.

MIME是电子邮件协议的一个扩展，它允许其他类型的数据在互联网上传送，就像视频、音频以及图片和应用程序。

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So the mail protocol never considered any type of authentication.

FORBES: Authenticate This!

The law-enforcement official said all of the mayor's mail is sorted and handled in several off-site facilities, and mail sent to the mayor's home goes through the same screening protocol.

WSJ: Letters to Mayor Bloomberg Tested Positive for Ricin

"Even with the new normal of being informal, the proper way to start an e-mail is with 'Dear, '" said Cynthia Lett, director of the Lett Group, a protocol training company in Silver Spring, Maryland.

CNN: Is 'Dear' dead?