Dual ISP, Dual Network Cards - how prioritize?

The problem is probably that any computer can only have one default gateway. As long as you are trying to reach an IP address that is on the same subnet of any one of your ip addresses you should be find. I assume that the network/email address you are trying to get to is located on a seperate subnet (i.e. there is a router between you and these addresses)
If this is the case then once your computer tries to find an IP that is outside of its own subnets on either IP address then it sends it to the Default Gateway.

You can get arround this by setting a static route in your computer that applies to the subnets within your company
basically manually sets the router that it shoud go to.

First you need to bring up a command promt and with your company's Network only plugged in, type in 'ipconfig' and note the default gateway.
then you need to do a ROUTE ADD -p. type ROUTE /? to get the syntax
you will need to know the network address (which you can probably determine by looking at your own IP and subnet mask from the ipconfig - or ask your Network Admin) and the MASK

If you give me the results of the ipconfig. I could take an educated guess at what the exact syntax of the ROUTE ADD would be

Plug your DSL Inside Interface into your corporate network and give it an IP address from your corporate network.  Adjust the route table in your corporate router to point it’s default gateway (sometimes called the last resort route) out the DSL’s Inside Interface IP address.

The default Gateway should always point to the interface that gives you access to most addresses and this is for the foreseeable future your Internet connection. As mentioned above, the 'route -p add' command should then be used to direct traffic for your internal subnets to the IP address of your internal router.

route -p (makes it remembered every time you reboot) 10.5.0.0 mask 255.255.0.0 ip_of_internal_router
route -p add 192.168.9.0 mask 255.255.255 ip_of_internal_router

In Internet Explorer open the Tools, Internet options, connections, LAN settings.


(I have made an assumption that you are using a Proxy server). Select Advanced.

In the exceptions section ad  in the network portion of any web servers/Intranet servers you may have on the internal lan.

192.168.*;10.*  

This will allow you to default to the Internet but still get to normal traffic and any internal http/https sites etc.

HTH