Cisco Cisco Email Security Appliance C170 Guia Do Utilizador

If configuring the MX/MTAs to include a custom header containing the sending IP address is not an 
option, you can configure the incoming relays feature to attempt to determine the sending IP address by 
examining the “Received:” headers in the message. Using the “Received:” header will only work if the 
number of network “hops” will always be constant for an IP address. In other words, the machine at the 
first hop (10.2.3.5 in 

) should always be the same number of hops away from the edge of your 

network. If incoming mail can take different paths (resulting in a different number of hops, as described 
in 

) to the machine connecting to your Cisco appliance, you must use a custom header (see 

Specify a parsing character or string and the number of network hops (or Received: headers) back to 
look. A hop is basically the message travelling from one machine to another (being received by the Cisco 
appliance does not count as a hop. See 

 for more information). AsyncOS looks for the first IP address following the first occurrence 

of the parsing character or string in the Received: header corresponding to the number of specified hops. 
For example, if you specify two hops, the second Received: header, working backward from the Cisco 
appliance is parsed. If neither the parsing character nor a valid IP address is found, the Cisco appliance 
uses the real IP address of the connecting machine.

For the following example mail headers, if you specify an opening square bracket (

[

) and two hops, the 

IP address of the external machine is 7.8.9.1. However, if you specify an closing parenthesis (

)

) as the 

parsing character, a valid IP address will not be found. In this case, the Incoming Relays feature is treated 
as disabled, and the IP of the connecting machine is used (10.2.3.5).

In the example in 

C

D