sendmail, 4th Edition

Rule Sets and m4

When building a configuration file using the m4 technique (The m4 Preprocessor on page 584) sendmail reserves certain rule set numbers and names 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 (now called parse through canonify) directly, and other rule sets indirectly (see Table 17-2 on page 595).

The configuration file created with the m4 technique uses quite a few rule sets beyond the base group. To avoid name collisions, we recommend that you begin all your own named rules with a leading capital letter.