Cisco Cisco Email Security Appliance C690 User Guide
Chapter 4 Validating Recipients Using an SMTP Server
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Cisco IronPort AsyncOS 7.5 for Email Advanced Configuration Guide
OL-25137-01
SMTP call-ahead recipient validation to allow the Email Security appliance to
query the SMTP server and validate the recipient before continuing the SMTP
conversation.
query the SMTP server and validate the recipient before continuing the SMTP
conversation.
SMTP call-ahead recipient validation allows the Email Security appliance to save
a significant amount of processing on messages for invalid recipients. In normal
processing, a message for an invalid recipient must be processed through the work
queue phases of the email pipeline before it can be dropped. Using the SMTP
call-ahead recipient validation feature, an invalid message can be dropped or
bounced during the incoming/receiving part of the email pipeline without
requiring additional processing.
a significant amount of processing on messages for invalid recipients. In normal
processing, a message for an invalid recipient must be processed through the work
queue phases of the email pipeline before it can be dropped. Using the SMTP
call-ahead recipient validation feature, an invalid message can be dropped or
bounced during the incoming/receiving part of the email pipeline without
requiring additional processing.
When you configure your Email Security appliance for SMTP call-ahead recipient
validation, the Email Security appliance suspends the SMTP conversation with
the sending MTA while it “calls ahead” to the SMTP server to verify the recipient.
When the IronPort appliance queries the SMTP server, it returns the SMTP
server’s response to the Email Security appliance, and depending on the settings
you have configured, you can accept the mail or drop the connection with a code
and custom response.
validation, the Email Security appliance suspends the SMTP conversation with
the sending MTA while it “calls ahead” to the SMTP server to verify the recipient.
When the IronPort appliance queries the SMTP server, it returns the SMTP
server’s response to the Email Security appliance, and depending on the settings
you have configured, you can accept the mail or drop the connection with a code
and custom response.
shows the basic workflow of the SMTP call-head validation
conversation.