Mail Gateway

The mail gateway is a machine that handles connections between networks running different communications protocols or communications between different networks using the same protocol. For example, a mail gateway might connect a TCP/IP network to a network running the Systems Network Architecture (SNA) protocol suite.

The simplest mail gateway to set up is one that connects two networks that use the same protocol or mailer. This system handles mail with an address for which sendmail cannot find a recipient in your domain. If a mail gateway exists, sendmail uses it for sending and receiving mail outside your domain.

You can set up a mail gateway between two networks using unmatched mailers, as shown in Figure 1-2. To support this, you must customize the sendmail.cf file on the mail gateway system, which can be a difficult and time-consuming process.

Figure 1-2 Gateway Between Different Communications Protocols

If you have to set up a mail gateway, you should find a gateway-configuration file that is close to what you need and modify it to fit your situation.

If you have a machine providing connections to the Internet, you can configure that machine as the mail gateway. Carefully consider your site's security needs before you configure a mail gateway. You might need to create a firewall gateway between your corporate network and the outside world, and set that up as the mail gateway.