When a header is checked using the $>+ in an
H configuration command (Section 25.5.1), the unaltered value of the header is stored
in the ${currHeader} macro and the length of that
header's unaltered value is stored in this
${hdrlen} macro. Note that the value stored in
${currHeader} will be truncated to MAXNAME (MAX...) characters, the default for which is 256. If
the header's value was longer than MAXNAME
characters, the number of characters stored in
${currHeader} will differ from the value stored in
${hdrlen}. For an illustration of one way to use
this macro, see Section 25.5.1.1.
${hdrlen} is transient. If it is defined in the
configuration file or in the command line, that definition can be
ignored by sendmail. Note that a
$& prefix is necessary when you reference this
macro in rules (that is, use $&{hdrlen}, not
${hdrlen}).
