Does Zimbra need a WAN IP adderess, or can it sit within a LAN with port forwarding enabled. So the zimbra server has a LAN IP or does it need two WAN IP's for the network with the domains, "domain.com" & "mail.domian.com" - with "domain.com" having the MX record of mail.domain.com? Or can the two domains be the same host?
I've tried searching the forums and wiki, but have had limited joy. If the single IP option is available with port forwarding, to receive external email, just port 25 needs to be open?