Have a 'new' mailserver running postfix on Ubuntu.

We are having some problems configuring the subnets & interfaces.

Basically 2 subnets (.253. & .254.) need to be connected through the 3rd subnet (.252.) where the Router is residing.

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet static
        address 10.62.254.199
        netmask 255.255.0.0
        network 10.62.254.0
        broadcast 10.62.255.255
        #gateway 10.62.252.138
        # dns-* options are implemented by the resolvconf package, if installed
        dns-nameservers 10.62.252.138
        dns-search ***.com

auto eth1
iface eth1 inet static
        address 10.62.253.199
        netmask 255.255.0.0
        network 10.62.253.0
        broadcast 10.62.255.255
        #gateway 10.62.252.138
        #dns-nameservers 10.62.254.199 10.62.253.199 10.62.252.199
        dns-nameservers 10.62.252.138
        dns-search ***.com


auto eth2
iface eth2 inet static
        address 10.62.252.199
        netmask 255.255.0.0
        network 10.62.252.0
        broadcast 10.62.255.255
        gateway 10.62.252.138
        #dns-nameservers 10.62.254.199 10.62.253.199 10.62.252.199
        dns-search ***.com

I have an external support company who are looking into this (they built and configured this server), but it's taking far too long... So I'm looking to highlight the mistake!