lhs rhs comment
The first line, the
S0, declares the start of rule set 0.
All the lines
S line and beginning with
belong to that rule set. A new rule set begins when another
line with a different number appears.
 If another
Sline appears with the same number, sendmail will print a warning. Prior to V8.7, the second definition wiped out the first. Beginning with V8.7, the second rule set's rules are appended to the rules of the first.
R line is a separate rule in the series of rules that
form a rule set. In the sendmail.cf 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 commenttab tab
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, but you must use tabs to separate the parts.
The leftmost part of the rule is called the LHS, for left-hand side.
The middle part is called the RHS,
for right-hand side.
These form the rule. A
comment 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 if-then pair. If the LHS evaluates to true, the RHS is evaluated. If the LHS evaluates to false, sendmail skips to the next rule in the rule set (if there is one):
if true do this R
rhsotherwise, go to next rule