Linux Network Administrator's Guide, Second Edition

The sendmail.cf and sendmail.mc Files

The m4 macro processor program generates the sendmail.df file when it processes the macro configuration file provided by the local system administrator. Throughout the remainder of this chapter we will refer to this configuration file as the sendmail.mc file.

The configuration process is basically a matter of creating a suitable sendmail.mc file that includes macros that describe your desired configuration. The macros are expressions that the m4 macro processor understands and expands into the complex sendmail.cf syntax. The macro expressions are made up of the macro name (the text in capital letters at the start), which can be likened to a function in a programming language, and some parameters (the text within brackets) that are used in the expansion. The parameters may be passed literally into the sendmail.cf output or may be used to govern the way the macro processing occurs.

A sendmail.mc file for a minimal configuration (UUCP or SMTP with all nonlocal mail being relayed to a directly connected smart host) can be as short as 10 or 15 lines, excluding comments.

Two Example sendmail.mc Files

If you’re an administator of a number of different mail hosts, you might not want to name your configuration file sendmail.mc. Instead, it is common practice to name it after the host—vstout.m4 in our case. The name doesn’t really matter as long as the output is called sendmail.cf. Providing a unique name for the configuration file for each host allows ...