How do I setup machine to direct port 25 traffic to a particular NIC in a dual-homed machine

My company uses TrendMicro's Interscan Viruswall for our email gateway.  Right now, it is running on a dedicated machine with an internal address of x.x.x.11.  Our website runs on a machine with an internal address of x.x.x.4.  Our Pix directs port 80 & 443 to x.x.x.4 and port 25 to x.x.x.11.

I want to decommission the dedicated Interscan machine and move the gateway to my webserver box which has dual NICs.  I have reconfigured my Exchange SMTP virtual server to use port 26 internally, and have configured both my old Interscan boxes to forward mail to Exchange on port 26.  

I have been able to recieve incoming email OK in this configuration, but have not been able to get outgoing to send from the webserver.  It seems that the machine wants to send using the x.x.x.4 NIC which our Pix is blocking.  Short of changing my firewall rules, is there a way to tell Server 2003 R2 to use NIC x.x.x.11 for port 25 traffic and x.x.x.4 for web traffic?
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To the best of my knowledge, outbound traffic always goes out as the primary NIC and/or primary IP address (in the event of a single NIC with multiple IP addresses assigned). I am afraid you will need to change your firewall rules to allow .4 to send mail out. Just to make sure I am understanding, you shutdown the old .11 box and have assigned the .11 address to the second NIC on the web server. I know it works mostly, but in the past, it has been recommended not to have two NIC's in the same box on the same segment/subnet/etc. because you have issues about source and the like. If you are going to have 2 NIC's on a single subnet/segment/etc. then you need to use some kind of "teaming" software to allow the NIC's to work together as a single IP address. I think the primary thing about this is the source IP always being one NIC and not the one that you invariably want it to be.

Just my thoughts...


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