How Cisco Ironport picks an outgoing IP address if there are many on the same subnet
If your IronPort is configured with multiple IP addresses on the same subnet and you wonder which one is used then Cisco has an answer for you:
Q: Which is the default used IP address (AUTO) if there are multiple IP addresses on the same subnet?
A: If there are multiple IP addresses configured within the same subnet as the default gateway, the IP address with the lowest number based on a c-string search will be used.
More details with the example are available at Cisco Email Security Appliance section of www.cisco.com web site.
So before adding a new one make sure that the default interface has been defined either by a content/message filter, deliveryconfig or alt-src host action. Assume that altsrchost CLI command should be good too.
P.S. Tagged this post as FreeBSD only because Cisco IronPort is based on FreeBSD