Cisco Cisco Email Security Appliance X1070 Information Guide
Contents
Introduction
What is a listener?
Related Information
Introduction
This document describes the term listener, as used in the Email Security Appliance (ESA).
What is a listener?
Note: This information is provided as a courtesy. It is recommended that you review the
associated with the AsyncOS version that your ESA currently runs for full details on
listeners. Refer to the "Configuring the Gateway to Receive Email" chapter.
The appliance functions as the email gateway for your organization as it services email
connections, accepts messages, and relays them to the appropriate systems. The appliance can
service email connections from the Internet to recipient hosts inside your network, and from
systems inside your network to the Internet. Typically, email connection requests use Simple Mail
Transfer Protocol (SMTP). The appliance services SMTP connections by default and acts as the
SMTP gateway, also known as a mail exchanger or "MX" for the network.
connections, accepts messages, and relays them to the appropriate systems. The appliance can
service email connections from the Internet to recipient hosts inside your network, and from
systems inside your network to the Internet. Typically, email connection requests use Simple Mail
Transfer Protocol (SMTP). The appliance services SMTP connections by default and acts as the
SMTP gateway, also known as a mail exchanger or "MX" for the network.
The appliance uses listeners in order to service incoming SMTP connection requests, A listener
describes an email processing service that is configured on a particular IP interface. Listeners
apply to email that enters the appliance, from either the Internet or from systems within your
network that try to reach the Internet. Use listeners to specify criteria that messages and
connections must meet in order to be accepted and for messages to be relayed to recipient hosts.
You can think of a listener as an "SMTP daemon" that runs on a specific port for each IP address
specified. Also, listeners define how the appliance communicates with systems that try to send
email to the appliance.
describes an email processing service that is configured on a particular IP interface. Listeners
apply to email that enters the appliance, from either the Internet or from systems within your
network that try to reach the Internet. Use listeners to specify criteria that messages and
connections must meet in order to be accepted and for messages to be relayed to recipient hosts.
You can think of a listener as an "SMTP daemon" that runs on a specific port for each IP address
specified. Also, listeners define how the appliance communicates with systems that try to send
email to the appliance.
You can create these types of listeners:
Public - Listens for and accepts email messages that come in from the Internet. Public
listeners receive connections from many hosts and direct messages to a limited number of
recipients.
listeners receive connections from many hosts and direct messages to a limited number of
recipients.
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Private - Listens for and accepts email messages that come from systems within the network,
typically from internal groupware and email servers (POP/IMAP), intended for recipients
outside the network in the Internet. Private listeners receive connections from a limited
(known) number of hosts and direct messages to many recipients.
typically from internal groupware and email servers (POP/IMAP), intended for recipients
outside the network in the Internet. Private listeners receive connections from a limited
(known) number of hosts and direct messages to many recipients.
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You can configure listeners from the appliance GUI (Network > Listeners) or from the appliance
CLI (listenerconfig).
CLI (listenerconfig).
Consider these rules and guidelines when you work with and configure listeners on the appliance:
You can define multiple listeners per configured IP interface, but each listener must use a
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