Hi I have to install a Firewall between two private Networks. The "big" net is a Win NT4.0-Domain ( Netbios over TCP/IP)for the administration of a company, with a gateway to an Internet provider. The "little" one is a own Win NT4.0-Domain, running a medicine net (Netbios over TCP-IP). Today these nets are physikaly separated. We want to connect both nets via a firewall. There should be a possibility for the users of the med-net, to use the internet-gateway (only http and ftp) with a proxy. (That´s not the problem!) On the other side, there is a MS-Exchange-Server in the "big" net , on which the Members of the medicine-net should paticipate (MS-Mail!). We don´t want to buy another exchange server. There should be no possibility connections from the outer net to the med-net. The domains will remain separated. I want to realize it with ipchains. But: What are the port-numbers which MS-Mail is using? Is MS-Mail only using net-bios? (Another idea is to install a sendmail-server and to change the mails with the exchange server with internet-mail protocoll, but this is not the plan of the bosses... :-( ) Who realized such a firewall? Who can give me some hints? Thanks a lot for your help Thomas Zinner