Руководство Пользователя для Cisco Cisco Email Security Appliance C170

For more information about Alias Tables, see “Creating Alias Tables” in the 
“Configuring Routing and Delivery Features” chapter of the Cisco IronPort 
AsyncOS for Email Advanced Configuration Guide.

You can use your existing LDAP infrastructure to define how the recipient email 
address of incoming messages (on a public listener) should be handled during the 
SMTP conversation or within the workqueue. See “Accept Queries” in the 
“Customizing Listeners” chapter of the Cisco IronPort AsyncOS for Email 
Advanced Configuration Guide. This allows the Cisco IronPort appliance to 
combat directory harvest attacks (DHAP) in a unique way: the system accepts the 
message and performs the LDAP acceptance validation within the SMTP 
conversation or the work queue. If the recipient is not found in the LDAP 
directory, you can configure the system to perform a delayed bounce or drop the 
message entirely.

For more information, see the “LDAP Queries” chapter in the Cisco IronPort 
AsyncOS for Email Advanced Configuration Guide.

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 Cisco IronPort appliance queries the SMTP server, it returns the SMTP 
server’s response to the Email Security appliance. The Email Security appliance 
resumes the SMTP conversation and sends a response to the sending MTA, 
allowing the conversation to continue or dropping the connection based on the 
SMTP server response (and settings you configure in the SMTP Call-Ahead 
profile).

For more information, see the “Validating Recipients Using an SMTP Server” 
chapter in the Cisco IronPort AsyncOS for Email Advanced Configuration Guide.