Cisco Cisco Email Security Appliance C170 Guia Do Utilizador

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.

The Work Queue is where the received message is processed before moving to the delivery phase. 
Processing includes masquerading, routing, filtering, safelist/blocklist scanning, anti-spam and 
anti-virus scanning, Outbreak Filters, and quarantining.

Data loss prevention (DLP) scanning is only available for outgoing messages. For information on where 
DLP message scanning occurs in the Work Queue, see 

.

Note, as a general rule, changes to security services (anti-spam scanning, anti-virus scanning, and 
Outbreak Filters) do not affect messages already in the work queue. As an example:

If a message bypasses anti-virus scanning when it first enters the pipeline because of any of these 
reasons:

anti-virus scanning was not enabled globally for the appliance, or

the HAT policy was to skip anti-virus scanning, or

there was a message filter that caused the message to bypass anti-virus scanning,