Introducing the m4 Macro Processor
Although Solaris provides prebuilt default configuration files for sendmail, these configuration files make certain assumptions about the e-mail architecture of a site that may not be true for your site. Because these assumptions are not documented and often have subtle side effects, it is best to build your own sendmail configuration file(s) with the prepackaged m4 macros provided with the sendmail distribution. When you do so, you can design the e-mail architecture for your entire site and implement it the way you want.
This section is a basic introduction to the m4 macro processor, and not a comprehensive ...