29.2 Rule Sets and m4

When building a configuration file using the m4 technique (see Section 19.1, "The m4 Preprocessor"), sendmail reserves certain rule-set numbers for its own use. Using the m4 technique, you can add rules to those rule sets, but you cannot replace those rule sets with your own. A few m4 keywords are available to make adding rules easier. They affect rule sets 0 through 3 directly and other rule sets indirectly (see Table 19.5 in Section 19.4.3, "Rules and rule sets").

The configuration file created with the m4 technique uses quite a few rule sets beyond the base group of 0 through 5. Table 29.1 shows all the rule sets used by the bare bones m4 technique. They are listed numerically, which also just happens to group them by function. The table also includes the name of the file containing the rules for each rule set.