🚀 go-pugleaf

I have just realised that anyone on our machine which is a Pyramid
running IDA sendmail 5.61 (or any of the suns in the campus running
sun standard 4.0.3 supplied sendmail) that it is possible to forge a
message to make it appears as if it came from someone else.  This is
because sendmail allows the forger to change From, and Sender fields.
Looking at the delivered mail I cannot find any tell tales that would
reveal the identity of the forger.  How can I stop this?

extra info:

The sendmail.cf does not contain the forger in its trused list of
users.  The sendmail is setuid to root and the default user in the .cf
file is 16 (mailer) and group is daemon

password file entry for mailer

	mailer:DISABLED:16:1:Mailer:/:/bin/false

Relevent bits of my sendmail.cf

############################################################
#
#	General configuration information
#
############################################################

DVUK-2.1


##########################
###   Special macros   ###
##########################

# my name
DnPOSTMASTER
# UNIX header format
DlFrom $g $d remote from $U
# delimiter (operator) characters (note '~' has been added)
Do.:%@!^=/[]~
# format of a total name
Dq$?x$x <$g>$|$g$.
# SMTP login message
De$j Sendmail $v/$V ready at $b

###################
###   Options   ###
###################

# location of alias file
OA/usr/lib/aliases
# default delivery mode (deliver in background)
Odbackground
# mail to me too (needed for multihost sites)
Om
# (don't) connect to "expensive" mailers
#Oc
# automatically do newaliases when aliases.dbm out of date
#OD
# temporary file mode 
OF0644
# default GID
Og1
# location of help file
OH/usr/lib/sendmail.hf
# log level
OL9
# default messages to old style
Oo
# Cc my postmaster on error replies I generate
#OP`'POSTMASTER
# queue directory
OQ/usr/spool/mqueue
# read timeout -- violates protocols
Or30m
# status file
OS/usr/lib/sendmail.st
# queue up everything before starting transmission
# Os
# default timeout interval
OT3d
# time zone names (V6 only)
# OtGMT,BST
# default UID
Ou16
# wizard's password
OWz3GvK.dPUxieQ
# load averages at which to start queuing/refuse connections
Ox6
OX8
# penalty per recipient
Oy1000
# memory-poor environmenet
OY
# boost for high-priority messages
#Oz1800
# generic names database
OKG/usr/local/admin/sendmail/tabs/generic.names
# penalty for being retried
#OZ0

###############################
###   Message precedences   ###
###############################

Pfirst-class=0
Pspecial-delivery=100
Pjunk=-100

#########################
###   Trusted users   ###
#########################

Troot
Tdaemon
Tmailer
Tuucp
Tmail

#############################
###   Format of headers   ###
#############################

H?F?From: $q
H?D?Date: $a
H?M?Message-Id: <$p.$t@$j>
H?F?Resent-From: $q
H?D?Resent-Date: $b
H?M?Resent-Message-Id: <$p.$t@$j>
HSubject:
HReceived: $?sfrom $s by $j; $b$.
HVia: $?S$S; $b$
  :
  :
Mlocal,   P=/bin/mail, F=lsmFD, S=20, R=20, A=mail -r $f -d $u 
Mbinmail, P=/bin/mail, F=lsmFD, S=20, R=20, A=mail -r $f -d $u 
Mprog,    P=/bin/sh,   F=nlsFD,   S=20, R=20, A=sh -c $u 
  :
Mether,	P=[IPC], F=nsmFDMuXC, S=21, R=21, A=IPC $h