Cisco Cisco Email Security Appliance C190 Technical References

The listenerconfig command allows you to create, edit, and delete a listener. 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 define and enforce your mail flow 
policies. Listeners also define how the appliance communicates with the system that is injecting email.

Commit: This command requires a ‘commit’.

Cluster Management: This command can be used in all three machine modes (cluster, group, machine).

Batch Command: This command supports a batch format.

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

Listeners are assigned to IP interfaces. All IP interfaces must be 
configured using the 

systemstartup

 command or the 

interfaceconfig

 command before you create and assign a listener 

to it.

The mail protocol is used for email receiving: either ESMTP or 
QMQP

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

Public

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.

Private

Blackhole

“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 Chapter 9, “Testing and 
Troubleshooting” of the Cisco AsyncOS for 
Email User Guide for more information.