=======================================
spamassassin -P -t -D < spam.example
=======================================
# transport and director
# in main config - add spamkill to trusted users
trusted_users = "root:exim:spamkill"

# in transports....
# Spam Assassin
spamcheck:
  driver = pipe
  command = /usr/sbin/exim -oMr spam-scanned -bS
  transport_filter = /usr/bin/spamc -s 500000
  home_directory = "/home/spamkill"
  current_directory = "/home/spamkill"
  # must use a privileged user to set $received_protocol on the way back in!
  user = spamkill
  group = spamkill
  log_output = true
  return_fail_output = true
  bsmtp = all
  return_path_add = false


# in directors
# Spam Assassin
spamcheck_director:
  # When to scan a message :
  #   -   it isn't already flagged as spam
  #   -   it isn't already scanned
  #   -   it didn't originate locally (as long as I don't harbor spammers :-))
  condition = "${if and { {!def:h_X-Spam-Flag:} {!eq{$received_protocol}{spam-scanned}}} {1}{0}}"
  driver = smartuser
  transport = spamcheck
---------------
One other subtle point.  Your spamd must have the "-F 0" flag added to
stop it adding and messing around with From_ headers.
=======================================