Macros that are given values while sendmail processes mail may not
get the value expected.
If that happens, careful hand-tracing of rule sets is required
to find the fault. For example, the value in
$g (see Section 31.10.16, $g)
is the result of
sender address rewriting and rewriting by
the rule set that is specified in the
equate of the selected delivery agent. Because
$g is used
to define the
From: header line, errors in that line
should be traced through errors in the
S= equate's rule
Macros can have other macros as their values. The sendmail program expands macros recursively. As a consequence, unintentional loops in macro definitions can cause sendmail to appear to hang and to eventually segmentation fault and core dump.