It is recommended that you
avoid adding, changing, or deleting listeners on Cloud Email Security
functions as the email gateway for your organization, servicing email
connections, accepting messages, and relaying them to the appropriate systems.
The appliance can service email connections from the Internet to recipients
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
service incoming SMTP connection requests, A listener describes an email
processing service that is configured on a particular IP interface. Listeners
apply to email entering the appliance, from either the Internet or from systems
within your network trying 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” running 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 the
following types of listeners:
Public. Listens for and accepts email
messages coming in from the Internet. Public listeners receive connections from
many hosts and direct messages to a limited number of recipients.
Private. Listens for and accepts email
messages coming 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.
When you create a
listener, you also must specify the following information:
Listener properties. Define global properties
that apply to all listeners, and properties specific to each listener. For
example, you can specify the IP interface and port to use for a listener, and
whether it is a public or private listener. For details on how to do this, see
Working with Listeners.
Which hosts that are allowed to connect to the
listener. Define a set of rules that control incoming connections
from remote hosts. For example, you can define remote hosts and whether or not
they can connect to the listener. For details on how to do this, see
Defining Which Hosts Are Allowed to Connect Using the Host Access Table.
(Public listeners only) The local domains for which the
listener accepts messages. Define which recipients are accepted by
the public listener. For example, if your organization uses the domain
currentcompany.com and it previously used
oldcompany.com , then you might accept messages for
both currentcompany.com and
oldcompany.com . For details on how to do this, see
Accepting or Rejecting Connections Based on Domain Name or Recipient Address.
configured in the listener, including its Host Access Table and Recipient
Access Table, affect how the listener communicates with an SMTP server during
the SMTP conversation. This allows the appliance to block a spamming host
before the connection is closed.
Figure 1. Relationship
between Listeners, IP Interfaces, and Physical Ethernet