Each rule set may contain zero or more individual rules.
Rules begin with the
configuration command, and each rule is
composed of three parts:
lhs rhs comment
The first line, the
, declares the start of rule set 0.
All the lines
line and beginning with
belong to that rule set. A new rule set begins when another
line with a different number appears.
line is a separate rule in the series of rules that
form a rule set. In the
files of major mail-handling
sites, a given rule set can have a huge number of
our hypothetical rule set 0 will have only one rule
and hence only one line that begins with an
lhs rhs optional comment
Each rule has three distinct parts, each divided from the others
by one or more tab characters.
You can use space characters inside each part,
use tabs to separate the parts.
The leftmost part of the rule is called the LHS, for
The middle part is called the RHS,
These form the rule. A
may optionally follow
the RHS and (if present) must be separated from the RHS by one or more tab
The LHS and RHS form an
pair. If the LHS evaluates
to true, the RHS is evaluated. If the LHS evaluates to false,
skips to the next rule in the rule set (if there is one):
if true do this
otherwise, go to next rule