/var/list/.bin/sendmails is in smartlist 3.15-22.
This file is owned by list:list, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44  | #! /bin/sh
: &&O='cd .' || exec /bin/sh "$0" $argv:q # we're in a csh, feed myself to sh
$O || exec /bin/sh "$0" "$@"		  # we're in a buggy zsh
#########################################################################
#	sendmails	Poor man's sendmail.				#
#									#
#	If you only have /bin/[r]mail and lack a sendmail compatible	#
#	mailer (i.e. a mailer that understands the -t option).		#
#									#
#	Created by S.R. van den Berg, The Netherlands			#
#########################################################################
#$Id: sendmails,v 1.6 1995/03/20 14:50:22 berg Exp $
test=test		# /bin/test
echo=echo		# /bin/echo
sed=sed			# /bin/sed
rm=rm			# /bin/rm
formail=formail		# /usr/local/bin/formail
sendmail=/usr/sbin/sendmail		# Your substitute sendmail
SMparseheader=no
while $test $# != 0 &&
  case "$1" in
     -t) SMparseheader=yes;;	# We only parse the -t option
     -*) ;;			# Ignore all other options
     *) $test a = b;;		# False!
  esac
do
  shift
done
if $test $SMparseheader = yes
then
  umask 077
  TMPF=/tmp/sms.$$
  trap "$rm -f $TMPF;exit 1" 1 2 3 13 15
  $rm -f $TMPF
  $sendmail $* `$sed -n -e "w $TMPF" -e '1,/^$/ p' | $formail -xTo:` <$TMPF
  $rm -f $TMPF
else
  exec $sendmail $*
fi
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