Cisco Cisco Email Security Appliance C680 User Guide
Chapter 8 Anti-Spam
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Cisco IronPort AsyncOS 7.5 for Email Configuration Guide
OL-25136-01
Figure 8-14
Mail Relayed by MX/MTA — Variable Number of Hops
Received Header
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
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
take different paths (resulting in a different number of hops, as described in
) to the machine connecting to your Cisco IronPort appliance, you
must use a custom header (see
IronPort Email Security appliance
Firewall
MX
Sending
Machine
Machine
IP: 7.8.9.1
IP: 10.2.3.4
IP: 10.2.3.6
MTA
IP: 10.2.3.5
Hop 2
Hop 1
C
D