Ah right, you just want to collect your mail from your isp, thats easy, turn off your ebox and connect through your router, once you are sure that everything works, reconnect your ebox, restart and then turn off dns, the mailserver etc open the required ports on the firewall and you should be good to go. But if all you want is a fileserver, dhcp and a firewall, use dhcp from router and just install samba and some form of iptables gui, but it sounds to me you do not need anything like ebox, you just need an old computer running smoothwall ( believe me for a firewall, it is better than ebox) and a fileserver running samba, you will find these a lot more configurable from the CLI .
I repeat these are my opinions and I have removed ebox from my test server as I think it is trying to do too much and non of it brilliantly, for instance, virtual domains, anybody care to tell me how you set up a virtual user without making him/her an actual ebox user?