Cisco Cisco Email Security Appliance C160 Mode D'Emploi

The typical configuration scenario for the Email Security appliance is as follows: 

Interfaces - Only one of the three available Ethernet interfaces on the Email Security appliance is 
required for most network environments. However, you can configure two Ethernet interfaces and 
segregate your internal network from your external Internet network connection.

Public Listener (incoming email) - The public listener receives connections from many external 
hosts and directs messages to a limited number of internal groupware servers.

Accepts connections from external mail hosts based on settings in the Host Access Table (HAT). 
By default, the HAT is configured to ACCEPT connections from all external mail hosts.

Accepts incoming mail only if it is addressed for the local domains specified in the Recipient 
Access Table (RAT). All other domains are rejected.

Relays mail to the appropriate internal groupware server, as defined by SMTP Routes.

Private Listener (outgoing email) - The private listener receives connections from a limited 
number of internal groupware servers and directs messages to many external mail hosts.

Internal groupware servers are configured to route outgoing mail to the Cisco C- or X-Series 
appliance.

The Email Security appliance accepts connections from internal groupware servers based on 
settings in the HAT. By default, the HAT is configured to RELAY connections from all internal 
mail hosts.

You can segregate incoming and outgoing email traffic over separate listeners and on separate IP 
addresses. You can use Internet Protocol version 4 (IPv4) and version 6 (IPv6) addresses. However, the 
System Setup Wizard on the appliance supports initial configuration of the following configurations:

2 separate listeners on 2 logical IPv4 and 2 IPv6 addresses configured on separate physical 
interfaces

segregates incoming and outgoing traffic

you can assign an IPv4 and an IPv6 address to each listener

1 listener on 1 logical IPv4 address configured on one physical interface

combines both incoming and outgoing traffic

you can assign both an IPv4 and an IPv6 address to the listener