According to procmail's HISTORY file, procmail-3.12
introduced a new behavior with respect to group-writable
.procmailrc files and .procmailrc files located in
group-writable directories. Specifically, procmail ignores
such a .procmailrc unless GROUP_PER_USER has been defined in
config.h at compile-time.
The most recent procmail update packages (3.13.1) do not
have GROUP_PER_USER defined and fail to function properly on
Red Hat Linux systems.
*** This bug has been marked as a duplicate of 2290 ***