Cisco Cisco Email Security Appliance C160 Mode D'Emploi

Use the Network > SMTP Routes page (or the 

smtproutes

 command) to construct routes. When you 

create a new route, you first specify the domain or partial domain for which you want to create a 
permanent route. You then specify destination hosts. Destination hosts can be entered as fully-qualified 
hostnames or as IP addresses. IP addresses can be either Internet Protocol version 4 (IPv4) or version 6 
(IPv6). 

For IPv6 addresses, AsyncOS supports the following formats:

2620:101:2004:4202::0-2620:101:2004:4202::ff

2620:101:2004:4202::

2620:101:2004:4202::23

2620:101:2004:4202::/64

You can also specify a a special destination host of 

/dev/null

 to drop the messages that match the entry. 

(So, in effect, specifying 

/dev/null

 for the default route is will ensure that no mail received by the 

appliance is ever delivered.) 

A receiving domain can have multiple destination hosts, each assigned a priority number, much like an 
MX record. The destination host with the lowest number identifies as the primary destination host for 
the receiving domain. Other destination hosts listed will be used as backup.

Destinations with identical priority will be used in a “round-robin” fashion. The round-robin process is 
based on SMTP connections, and is not necessarily message-based. Also, if one or more of the 
destination hosts are not responding, messages will be delivered to one of the reachable hosts. If all the 
configured destination hosts are not responding, mail is queued for the receiving domain and delivery to 
the destination hosts is attempted later. (It does not fail over to using MX records). 

When constructing routes using the 

smtproutes

 command in the CLI, you can prioritize each destination 

host by using 

/pri=

, followed by an integer between 

0

 and 

65535

 to assign priority (

0

 is the highest 

priority) after the hostname or IP address. For example, 

host1.example.com/pri=0 

has a higher priority 

than 

host2.example.com/pri=10

. Separate multiple entries with commas.

You can define up to 40,000 routes. The final default route of 

ALL

 is counted as a route against this limit. 

Therefore, you can define up to 39,999 custom routes and one route that uses the special keyword 

ALL

. 

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