Cisco Cisco Email Security Appliance C160 Mode D'Emploi

Use the special keyword 

USEDNS

 to tell the appliance to do MX lookups to 

determine next hops for specific domains. This is useful when you need to route 
mail for subdomains to a specific host. For example, if mail to example.com is to 
be sent to the company’s Exchange server, you might have something similar to 
the following SMTP route: 

example.com exchange.example.com

However, for mail to various subdomains (foo.example.com), add an SMTP route 
that looks like this: 

.example.com USEDNS

Alerts sent from the appliance to addresses specified in the System 
Administration > Alerts page (or the 

alertconfig

 command) follow SMTP 

Routes defined for those destinations. 

Incoming: if one message has 10 recipients and they are all on the same Exchange 
server, AsyncOS will open one TCP connection and present exactly one message 
to the mail store, not 10 separate messages.

Outgoing: works similarly, but if one message is going to 10 recipients in 10 
different domains, AsyncOS will open 10 connections to 10 MTAs and deliver 
them one email each.

Splintering: if one incoming message has 10 recipients and they are each in 
separate Incoming Policy groups (10 groups), the message will splinter even if all 
10 recipients are on the same Exchange server. Thus, 10 separate emails will be 
delivered over a single TCP connection.