Cisco Cisco Email Security Appliance C160 Mode D'Emploi

4xx: An SMTP code starting with a 4 means that a temporary failure has occurred in processing the 
SMTP request. A retry may later be processed successfully. For example, a response of 451 means 
the requested action was aborted or there was a local error in processing. 

5xx: An SMTP code starting with 5 means a permanent failure in processing the SMTP request 
occurred. For example, a response of 550 means the requested action was not taken or the mailbox 
was unavailable.

Timeout. If no response is returned from the call-ahead server, you can configure how long to 
attempt to retry before a timeout occurs. 

Connection error. If a connection to the call-ahead server fails, you can configure whether to accept 
or reject a connection for the recipient address.

Once you create the SMTP Call-Ahead Server Profile, you need to enable it on a listener to allow the 
listener to validate incoming mail via the SMTP server. SMTP call-ahead functionality is only available 
on public listeners, as recipient validation is not necessary for private listeners.

To enable an SMTP Call-Ahead Server Profile on a listener:

Go to Network > Listeners.

Click the name of the listener where you want to enable SMTP call-ahead functionality.

The Edit Listener page opens.

In the SMTP Call Ahead Profile field, select the SMTP Call-Ahead profile you want to enable.