Sean advised Nick,
note what SWITCHRC does, especially "If the named rcfile doesn't exist or
is not a normal file or /dev/null then an error will be logged and
processing will continue in the current rcfile."
The man page phrases that poorly: if the named rcfie doesn't exist, or
if it exists but it is neither a normal file nor /dev/null, then an
error is logged and processing continues in the current rcfile.
But if SWITCHRC ius set to /dev/null, or to the name of a zero-size
readable plain file, or to a null string, or if you unset SWITCHRC by
having no equal sign at all, then procmail skips the rest of the current
rcfile and pops up one level of INCLUDERCs. If it wasn't down any
levels of INCLUDERCs, then it acts as though it ran out of recipes and
delivers to $DEFAULT (and if that fails, to $ORGMAIL).
I've never had administrative privileges anywhere and never toyed with
/etc/procmailrc, but I'm under the impression that if you unset SWITCHRC
there (or set it to /dev/null or to a null string), procmail skips the
rest of /etc/procmailrc, drops any special privileges, and heads for
$HOME/.procmailrc. If $HOME/.procmailrc doesn't exist or isn't usable,
procmail delivers to $DEFAULT (and if that fails, to $ORGMAIL).
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