I have a network that at the moment is isolated from the internet. We are going to connect it to an existing adsl line that has a firewall,but we want to add another firewall behind it as we do not have total control over the existing firewall. The only thing we want to allow is smtp access for one computer. Can we then just put in the new firewall and only open up for port 25 outgoing? The firewall that I want to use is a POWERBIT SAFEGATE FIREWALL IX78 is this an acceptable choice to use?
TCP 25 OPEN should be enough, however if you're dealing with only one server, you can limit the connection from that specific machine (PC) to that specific server; for the sake of extra security.
i think in your firewall there is a location that is related to your policy and in this situation there are a lot of features and services for controlling smtp,imap,http,ftp ,etc.you can use smtp settings part for solving this problem.in additional, behind this location you can limit your accessibility from a specific pc or specific server.