as one of the core applications of enterprise network, e-mail provides strong support for enterprises to exchange information. While bringing convenience to people, e-mail also brings security problems such as spam, password being cracked, and email being intercepted. With the development of secure e-mail technology, the security problems encountered by e-mail are being gradually resolved.

End-to-end secure e-mail technology

End-to-end secure e-mail technology ensures that the content cannot be modified and is undeniable during the whole process from sending to receiving. PGP and S/MIME are two mature end-to-end secure e-mail standards.

PGP(Pretty Good Privacy) is widely used. It uses one-way hash algorithm to sign the mail content to ensure that the mail content cannot be modified, and uses public key and private key technology to ensure that the mail content is confidential and undeniable. Both the sender's and the receiver's public keys are kept in public places, and the authority of the public key can be verified by a third party. In PGP system, trust is the direct relationship between both parties.