Cisco Cisco Email Security Appliance C170 Guia Do Utilizador

Enterprise Gateways (or Message Transfer Agents, i.e. MTAs) normally communicate “in the clear” over 
the Internet. That is, the communications are not encrypted. In several scenarios, malicious agents can 
intercept this communication without the knowledge of the sender or the receiver. Communications can 
be monitored and even altered by a third party. 

Transport Layer Security (TLS) is an improved version of the Secure Socket Layer (SSL) technology. It 
is a widely used mechanism for encrypting SMTP conversations over the Internet. AsyncOS supports the 
STARTTLS extension to SMTP (Secure SMTP over TLS), described in RFC 3207 (which obsoletes RFC 
2487).

The TLS implementation in AsyncOS provides privacy through encryption. It allows you to import an 
X.509 certificate and private key from a certificate authority service or create a self-signed certificate to 
use on the appliance. AsyncOS supports separate TLS certificates for public and private listeners, secure 
HTTP (HTTPS) management access on an interface, the LDAP interface, and all outgoing TLS 
connections.