#!/bin/sh
#
# filter-sideline.sh
#
# Simple filter to plug Anomy Sanitizer and SpamAssassin into
# the Postfix MTA, plus take action on very high scoring mail.
# "Action" includes sending to a holding directory for later inspection 
# ("sideline" it), diverting to another e-mail address, or deleting it.
#
# Note: SpamAssassin "scores" are not foolproof, but generally 
#       messages with score 10 and over are rarely legitimate mail.
#
# From http://advosys.ca/papers/postfix-filtering.html
# Advosys Consulting Inc., Ottawa
#
# For use with:
#    Postfix 20010228 or later
#    Anomy Sanitizer revision 1.49 or later
#    SpamAssassin 2.42 or later
#
# Note: Modify the file locations to match your particular
#       server and installation of SpamAssassin.

# File locations:
# (CHANGE AS REQUIRED TO MATCH YOUR SERVER)
INSPECT_DIR=/var/spool/filter
SENDMAIL="/usr/lib/sendmail -i"
ANOMY=/usr/local/anomy
ANOMY_CONF=/usr/local/anomy/anomy.conf
ANOMY_LOG=/dev/null
SPAMASSASSIN=/usr/bin/spamassassin
EGREP=/bin/egrep

# Directory to put high score spam into:
# (NOTE: Create this directory and give it same permissions as $INSPECT_DIR)
SIDELINE_DIR=/var/spool/spam

# Number of *'s in X-Spam-level header needed to sideline message:
# (Eg. Score of 5.5 = "*****" )
SPAMLIMIT=10

export ANOMY SPAMLIMIT

# Exit codes from <sysexits.h>
EX_TEMPFAIL=75
EX_UNAVAILABLE=69

cd $INSPECT_DIR || { echo $INSPECT_DIR does not exist; exit $EX_TEMPFAIL; }

# Clean up when done or when aborting.
trap "rm -f out.$$" 0 1 2 3 15

# Pipe message through SA to a temp file:
cat | $SPAMASSASSIN -L -x > out.$$

# Are there more than $SPAMLIMIT stars in X-Spam-Level header? :
if $EGREP -q "^X-Spam-Level: \*{$SPAMLIMIT,}" < out.$$
then
	# Option 1: Move high scoring messages to sideline dir so a human can look at them later:
	mv out.$$ $SIDELINE_DIR/`date +%Y-%m-%d_%R`-$$
	# Option 2: Divert to an alternate e-mail address:
	# (Comment out the above, then uncomment next line to use this option)
	# $SENDMAIL spamtrap@example.com < out.$$
	# Option 3: Delete the message (Not recommended)
	# rm -f out.$$
else
	$ANOMY/bin/sanitizer.pl $ANOMY_CONF < out.$$ 2>>$ANOMY_LOG | $SENDMAIL "$@" 
fi

exit 0