I have a machine hosted in datacenter with 3 network interfaces.
Interface network ip address eth0 192.168.1.0/24 192.168.1.10 eth1 192.168.2.0/24 192.168.2.10 eth2 192.168.3.0/24 192.168.3.10
My default gateway is set to 192.168.2.1, where I can access some services provided by datacenter (repositories, ntp and so on).
Network 192.168.1.0/24 has a gateway at 192.168.1.1 through which I can access outside world, where dragons live. When I need to go out of my server I simply add a static route. I kind of like this setting as I know where my server is connecting.
Now, I have a mail client (exim4) which needs to send mails... to anyone. So ideally it needs to have a default gw set to 192.168.1.1. Is there a way to route only traffic for this particular service or should I simply change my network configuration on the server?
I'm on debian 8 if that makes any difference.