Cisco Cisco Email Security Appliance C170 Guia Do Utilizador

SMTP Routes allow you to redirect all email for a particular domain to a different mail exchange (MX) 
host. For example, you could make a mapping from 

example.com

 to 

groupware.example.com

. This 

mapping causes any email with 

@example.com

 in the Envelope Recipient address to go instead to 

groupware.example.com

. The system performs an “MX” lookup on 

groupware.example.com

, and then 

performs an “A” lookup on the host,

 

just like a normal email delivery. This alternate MX host does not 

need to be listed in DNS MX records and it does not even need to be a member of the domain whose 
email is being redirected. The Cisco IronPort AsyncOS operating system allows up to forty thousand 
(40,000) SMTP Route mappings to be configured for your Cisco IronPort appliance. (See 

This feature also allows host “globbing.” If you specify a partial domain, such as 

.example.com

, then 

any domain ending in 

example.com

 matches the entry. For instance, 

fred@foo.example.com

 and 

wilma@bar.example.com

 both match the mapping.

If a host is not found in the SMTP Routes table, an MX lookup is performed using DNS. The result is 
not re-checked against the SMTP Routes table. If the DNS MX entry for 

foo.domain

 is 

bar.domain

, any 

email sent to 

foo.domain

 is delivered to the host 

bar.domain

. If you create a mapping for 

bar.domain

 

to some other host, email addressed to 

foo.domain 

is not affected. 

In other words, recursive entries are not followed. If there is an entry for 

a.domain 

to redirect to 

b.domain

, and a subsequent entry to redirect email for 

b.domain

 to 

a.domain

, a mail loop will not be 

created. In this case, email addressed to 

a.domain

 will be delivered to the MX host specified by 

b.domain

, and conversely email addressed to 

b.domain

 will be delivered to the MX host specified by 

a.domain

.

The SMTP Routes table is read from the top down for every email delivery. The most specific entry that 
matches a mapping wins. For example, if there are mappings for both 

host1.example.com

 and 

.example.com

 in the SMTP Routes table, the entry for 

host1.example.com

 will be used because it is the 

more specific entry — even if it appears after the less specific 

.example.com

 entry. Otherwise, the 

system performs a regular MX lookup on the domain of the Envelope Recipient.

You can also define a default SMTP route with the special keyword 

ALL

. If a domain does not match a 

previous mapping in the SMTP Routes list, it defaults to being redirected to the MX host specified by 
the 

ALL

 entry. 

When you print the SMTP Routes entries, the default SMTP route is listed as 

ALL:

. You cannot delete 

the default SMTP route; you may only clear any values entered for it.

Configure the default SMTP route via the Network > SMTP Routes page or the 

smtproutes

 command.

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