User Guide

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AsyncOS 9.1.2 for Cisco Email Security Appliances User Guide

Chapter 13 Anti-Spam

Determining Sender IP Address In Deployments with Incoming Relays

Step 4 Enter the IP address of the MTA, MX, or other machine that connects to the Email Security appliance to

relay incoming messages.

You can use IPv4 or IPv6 addresses, standard CIDR format, or an IP address range. For example, if you

have several MTAs at the edge of your network receiving email, you might want to enter a range of IP

addresses to include all of your MTAs, such as 10.2.3.1/8 or 10.2.3.1-10.

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

Step 5 Specify the header that will identify the IP address of the original external sender.

When entering a header, you do not need to enter the trailing colon.

a. Select the header type:

Choose custom headers (recommended) or Received headers.

b. For custom headers:

Enter the header name that you configured the relaying machine to add to relayed messages.

For example:

SenderIP

X-CustomHeader

c. For Received headers:

Enter the character or string after which the IP address will appear. Enter the number for the “hop”

to check for the IP address.

Step 6 Submit and commit your changes.

What To Do Next

Consider doing the following:

• Add the relaying machine to a sender group with a mail flow policy that has unlimited messages for

DHAP. For an explanation, see Incoming Relays and Directory Harvest Attack Prevention,

page 13-22.

• To facilitate tracking and troubleshooting, configure the appliance logs to show which header is

used. See Configuring Logs to Specify Which Headers Are Used, page 13-23.