Cisco Cisco Email Security Appliance C690 ユーザーガイド
23-10
Cisco AsyncOS 9.0 for Email User Guide
Chapter 23 Encrypting Communication with Other MTAs
Enabling TLS and Certificate Verification on Delivery
You can specify a certificate for the appliance to use for all outgoing TLS connections. To specify the
certificate, click Edit Global Settings on the Destination Controls page or use
certificate, click Edit Global Settings on the Destination Controls page or use
destconfig -> setup
in
the CLI. The certificate is a global setting, not a per-domain setting.
You can specify 5 different settings for TLS for a given domain when you include a domain using the
Destination Controls page or the
Destination Controls page or the
destconfig
command. In addition to specifying whether exchanges
with a domain are required or preferred to be TLS encoded, you can dictate whether validation of the
domain is necessary. See
domain is necessary. See
for an explanation of the settings.
Table 23-3
TLS Settings for Delivery
TLS Setting
Meaning
Default
The default TLS setting set using the Destination Controls page or the
destconfig -> default
subcommand used for outgoing connections from the
listener to the MTA for the domain.
The value “Default” is set if you answer “no” to the question: “Do you wish to
apply a specific TLS setting for this domain?”
apply a specific TLS setting for this domain?”
1. No
TLS is not negotiated for outgoing connections from the interface to the MTA
for the domain.
for the domain.
2. Preferred
TLS is negotiated from the Email Security appliance interface to the MTA(s) for
the domain. However, if the TLS negotiation fails (prior to receiving a 220
response), the SMTP transaction will continue “in the clear” (not encrypted). No
attempt is made to verify if the certificate originates from a trusted certificate
authority. If an error occurs after the 220 response is received the SMTP
transaction does not fall back to clear text.
the domain. However, if the TLS negotiation fails (prior to receiving a 220
response), the SMTP transaction will continue “in the clear” (not encrypted). No
attempt is made to verify if the certificate originates from a trusted certificate
authority. If an error occurs after the 220 response is received the SMTP
transaction does not fall back to clear text.
3. Required
TLS is negotiated from the Email Security appliance interface to MTA(s) for the
domain. No attempt is made to verify the domain’s certificate. If the negotiation
fails, no email is sent through the connection. If the negotiation succeeds, the
mail is delivered via an encrypted session.
domain. No attempt is made to verify the domain’s certificate. If the negotiation
fails, no email is sent through the connection. If the negotiation succeeds, the
mail is delivered via an encrypted session.