Cisco Cisco Email Security Appliance C160 Mode D'Emploi

Secure/Multipurpose Internet Mail Extensions (S/MIME) is a standards-based method for sending and 
receiving secure, verified email messages. S/MIME uses public/private key pair to encrypt or sign 
messages. This way, 

If the message is encrypted, only the message recipient can open the encrypted message. 

If the message is signed, the message recipient can validate the identity of the sender’s domain and 
can be assured that the message has not been altered while in transit.

For more information about S/MIME, review the following RFCs:

RFC 5750: Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2 - Certificate 
Handling

RFC 5751:   Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2 - Message 
Specification

RFC 3369: Cryptographic Message Syntax

Organizations may want to communicate securely using S/MIME without requiring that all end users 
possess their own certificates. For such organizations, Email Security appliance supports S/MIME 
security services (signing, encryption, verification, and decryption) at the gateway level using 
certificates that identify the organization rather than the individual user. 

Email Security appliance provides the following S/MIME security services for Business-to-Business 
(B2B) and Business-to-Consumer (B2C) scenarios:

Sign, encrypt, or sign and encrypt messages using S/MIME. See