Cisco Cisco Email Security Appliance C680 User Guide

The Network > Listeners page and the 

listenerconfig

 command in the CLI allow you to create, edit, 

and delete a listener. Cisco IronPort AsyncOS requires that you specify criteria that messages must meet 
in order to be accepted and then relayed to recipient hosts — either internal to your network or to external 
recipients on the Internet.

These qualifying criteria are defined in listeners; collectively, they ultimately define and enforce your 
mail flow policies. Listeners also define how the Cisco IronPort appliance communicates with the 
system that is injecting email. 

Each listener is composed of the criteria shown in 

.

In addition to these criteria, you can also configure the following for each listener:

SMTP Address Parsing Options (optional settings for controlling parsing in SMTP “MAIL FROM” 
and “RCPT TO,” see 

Advanced Configuration Options (optional settings for customizing the behavior of the Listener, see 

)

LDAP Options (optional settings for controlling LDAP queries associated with this Listener, see 

)

Unique nickname you supply for the listener, for future reference. The names you 
define for listeners are case-sensitive. AsyncOS will not allow you to create two 
identical listener names.

Listeners are assigned to IP interfaces. The IP interface is defined by the 

interfaceconfig

 command. Any IP interfaces must be configured using the 

System Setup Wizard or the 

systemsetup

 command or the IP Interfaces page (or 

the 

interfaceconfig

 command) before you create and assign a listener to it. The 

version of the Internet Protocol address of the interface determines the type of 
traffic the listener accepts. If the IP interface has both an IPv4 and IPv6 address, 
then the listener can accept connections from both IPv4 and IPv6 addresses.

The mail protocol to used for email receiving: either SMTP or QMQP (only 
available via the 

listenerconfig

 command in the CLI).

The specific IP port used for connections to the listener. By default, SMTP uses 
port 25 and QMQP uses port 628.

Public and private listeners are used for most configurations. By 
convention, private listeners are intended to be used for private 
(internal) networks, while public listeners contain default 
characteristics for receiving email from the Internet. 

“Blackhole” listeners can be used for testing or troubleshooting 
purposes. When you create a blackhole listener, you choose whether 
messages are written to disk or not before they are deleted. (See 
“Testing and Troubleshooting” in the Cisco IronPort AsyncOS for 
Email Daily Management Guide for more information.) Writing 
messages to disk before deleting them can help you measure the rate 
of receiving and the speed of the queue. A listener that doesn’t write 
messages to disk can help you measure the pure rate of receiving 
from your message generation systems. This listener type is only 
available through the 

listenerconfig

 command in the CLI.