Example Network
The majority of networks connected to the Internet look like the picture below. These are small, single-subnet networks connected to the Internet at a single point called a gateway.

The gateway may have different physical forms (a dedicated computer, a router, DSL modem, etc.) The feature common to all gateways is that they have at least two interfaces. One interface is connected to the internal network (we will call it inside interface), while the other (the ouside interface) is connected to the Internet, typically through an Internet Service Provider (ISP.) The Trilent Mail Proxy is usually installed on the gateway computer. |