I just need to confirm a few things.

The SBE 2.5 will be on the private side of a DLINK router

Do I need to install the Firewall if this is the case?

I assume I only open the ports on the dlink for the services I want to
get through?

email port 25
ifolder port (port ?)
remote administration port ?
openvpn port ?
groupwise web access port ?

Suggestions or recommendations?