Hi there, I need some advice on closing and open mail relay. The difficulty I am facing is that it is Exchange version 5. The server in question is an old SBS 4.0 server. The setup is as follows: Single server with one netcard. Private IP Address 10.x.x.x range Cisco801 router on 10.0.0.1 - router is using NAT My question is this; how do i configure Exch 5 to only allow specified smtp server ip's to connect to it? But if the NAT on the router translates all incomming addresses on port 25 then surely the exchange server will only ever see the originating address connecting to it as that of router's internal address. If this is the case, then should I bee looking at getting a hardware firewall? (as well as obviously upgrading the exchange server!) all comments gratefully appreciated. Richard Pettigrew Harkins & Anderson Ltd