This topic assumes that you have the Server Administration Tool open that you have selected and logged onto the server configuration that you want to change. If you are using the client (available with custom installations only), you can administer remote server configurations only.
You can use an IP address if your site uses only static IP addresses. The application uses SMTP, which traditionally operates over TCP using port 25. It is widely used and is the Internet’s standard host-to-host mail transport protocol.