37.11. Adding Sendmail Features with M4
The primary Sendmail configuration file sendmail.cf is extremely complex, and almost impossible to edit manually. Fortunately, it is usually built from a series of M4 macro files that are much simpler and can be modified using this module or by manual editing. M4, for those who have not heard of it before, is a program that parses text files and expands macros in them. These macros can include other text files, define variables and functions, or exclude text based on certain conditions. M4 is very similar to the preprocessor used by the C programming language which handles #include and #define statements. Fortunately, this module hides most of the complex details from you.
Often, the default Sendmail configuration ...
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