IBM Proventia Getting Started Manual page 16

Chapter 1: Introduction to the Appliance
Example of outgoing
mail traffic
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the appliance. Changes might also be possible on preceding mail relays,
load balancers, or content switches.
Make sure that all MX IP addresses for all internal domains
Important:
are routed through the appliance. The appliance works as an SMTP relay,
which is a Layer 7 device. The appliance does not forward or route IP
traffic; inline deployment is not a deployment option for the appliance.
If you need to change the DNS MX entries on your DNS
Important:
servers to new addresses, the DNS population over the Internet can take
up to three days (72 hours). Make sure you can re-route SMTP traffic on
MX IP addresses before you change any DNS records.
Even if you only want to scan incoming mail traffic, you
Important:
should still configure outgoing SMTP, which is used for email messages
generated from the appliance.
You should set up the appliance to inspect outgoing email messages from
your network, for example, configuring the appliance to check for
attachments, confidential content, or disclaimers that have been added to
outgoing mail.
Figure 5: An example of outgoing mail traffic through the appliance
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