You'd normally include only the macro definitions that were unique to your domain here, such as smart host definitions or relay hosts, but you are not limited to these. The sendmail source distribution comes with a number of sample domain macro files that you can use to model your own. These sendmail features make the supported configurations very simple to use. There are a large number, and throughout this chapter we'll talk about only a few of the more useful and important ones. You can find full details of the features available in the CF file included in the source package.
Some features take one optional parameter.
These are called local macro definitions . Many of them are listed in the CF file in the sendmail source package. The local macro definitions are usually invoked by supplying the name of the macro with an argument representing the value you wish to assign to the variable the macro manages. Again, we'll explore some of the more common local macro definitions in the examples we present later in the chapter. In our network we need the SMTP transport to send and receive mail among the hosts on our local area network, and the UUCP transport to send and receive mail from our smart host.