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Cisco Cisco Email Security Appliance C170 Guia Do Utilizador

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25-8
User Guide for AsyncOS 10.0 for Cisco Email Security Appliances
 
Chapter 25      Encrypting Communication with Other MTAs
  Enabling TLS on a Listener’s HAT
By default, neither private nor public listeners allow TLS connections. You must enable TLS in a 
listener’s HAT to enable TLS for either inbound (receiving) or outbound (sending) email. In addition, all 
default mail flow policy settings for private and public listeners have the 
tls
 setting set to “off.” 
You can assign a specific certificate for TLS connections to individual public listeners when creating a 
listener. For more information, see 
Related Topics
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•
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Assigning a Certificate to a Public or Private Listener for TLS Connections 
Using the GUI
Procedure 
Step 1
Navigate to the Network > Listeners page.
Step 2
Click the name of the Listener to edit.
Step 3
In the Certificate field, choose a certificate.
Step 4
Submit and commit your changes.
2. Preferred
TLS is allowed for incoming connections to the listener from MTAs. 
3. Required
TLS is allowed for incoming connections to the listener from MTAs, and until 
a 
STARTTLS
 command is received, the appliance responds with an error message 
to every command other than 
NOOP
, 
EHLO
, or 
QUIT
. This behavior is specified by 
RFC 3207, which defines the SMTP Service Extension for Secure SMTP over 
Transport Layer Security. “Requiring” TLS means that email which the sender 
is not willing to encrypt with TLS will be refused by the appliance before it is 
sent, thereby preventing it from be transmitted in the clear.
Table 25-2
TLS Settings for a Listener
TLS Setting
Meaning