Redundant Internet connections on different NICs to 2003 server

I'm trying to set up a Windows 2003 Exchange server to accept
connections from 2 different ISPs so email can still be received if one
of our ISPs goes down. I have three NICs in the server. The primary
Internet connection, with a default gateway to the primary Internet
router on a private subnet, the LAN connection on a seperate private
subnet, and the backup ISP on a third private subnet. The problem I'm
running into is the traffic on the backup connection getting routed out
through the primary connection because it has the default gateway. I
would like to be able to put a gateway on the backup Internet
connection that routes everything that enters the backup NIC back out
through the backup NIC to the backup Internet router. In other words,
I want the primary connection and the LAN to be able to communicate
with each other, but I want the backup connection to be completely
isolated from the two and to route all request that come in through the
backup NIC back to the router it came from. Is there an easy way to
set things up this way?

No, there isn't any easy way to do that. The router would need to be
able to route packets depending on where the original packet came from.
Win2003 certainly can't do it by itself. It only routes on the destination
address.

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ps.com...
> I'm trying to set up a Windows 2003 Exchange server to accept
> connections from 2 different ISPs so email can still be received if one
> of our ISPs goes down. I have three NICs in the server. The primary
> Internet connection, with a default gateway to the primary Internet
> router on a private subnet, the LAN connection on a seperate private
> subnet, and the backup ISP on a third private subnet. The problem I'm
> running into is the traffic on the backup connection getting routed out
> through the primary connection because it has the default gateway. I
> would like to be able to put a gateway on the backup Internet
> connection that routes everything that enters the backup NIC back out
> through the backup NIC to the backup Internet router. In other words,
> I want the primary connection and the LAN to be able to communicate
> with each other, but I want the backup connection to be completely
> isolated from the two and to route all request that come in through the
> backup NIC back to the router it came from. Is there an easy way to
> set things up this way?
>