I work for a school. We have a very simple setup with a Local Area Network connected with 3Com Superstack Switches. We have a CISCO Internet Access Router 1720. We have a mail server which has a local/private IP and there is a NAT rule defined on the router to redirect port 25 and port 110 to the mail server. Till now I am using only one public IP which is defined on router. In last few days we are experiencing a problem from AOL mail accounts. AOL doesn't accept our mails just becuase the mail server is running on private IP. I want to switch my mail server on a public IP and configure the firewall on the router as well. Could somebody please guide me how I can configure Cisco as a firewall and configure DMZ to allow the mail server to be accessed from Internet?