#!/bin/sh

# Postfix pipe transport destination for domain mail spam filtering.
# Copyright (c) 2010, John Morrissey <jwm@horde.net>
#
# This program is free software; you can redistribute it and/or modify it
# under the terms of Version 2 of the GNU General Public License as
# published by the Free Software Foundation
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
# Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA


# Dereferences aliases using $ALIAS_MAP and spam filters the message.
# Delivers non-spam to the dereferenced aliases and spam to $SPAM_RECIP,
# if defined.


# Needs corresponding Postfix configuration:
#
# master.cf:
#   spamassassin
#            unix  -       n       n       -       -       pipe
#     flags=Rq user=nobody argv=/usr/local/bin/proftpd-antispam ${sender} ${recipient}
#
# main.cf:
#   transport_maps = hash:/etc/postfix/transport
#   spamassassin_destination_recipient_limit = 1
#
# transport:
#   proftpd.org   spamassassin:


ALIAS_MAP=hash:/etc/postfix/aliases.proftpd.org
SPAMC_USER=proftpd
SPAM_RECIP=

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

export PATH="$PATH:/usr/sbin"

umask 077

if ! progname=$(basename "$0"); then
	logger -sp mail.warning -t "$0" 'Unable to determine \$progname.'
	exit $EX_TEMPFAIL
fi

usage="$progname SENDER RECIPIENT"

sender=$1
shift
if [ -z "$sender" ]; then
	echo "$usage"
	exit $EX_UNAVAILABLE
fi

# We'll support multiple incoming recipients here, but the formail
# Delivered-To injection below only supports a single incoming recipient.
# Postfix needs ${transportname}_destination_recipient_limit = 1 to limit
# deliveries to this transport to a single recipient.
recipients=''
for recip in "$@"; do
	if [ -z "$recip" ]; then
		echo "$usage"
		exit $EX_UNAVAILABLE
	fi

	# Map the incoming recipient to the alias destination. If we re-inject
	# the message to the original recipient address, we'll just hit ourselves
	# again and loop forever.
	recip=$(postmap -q "$recip" "$ALIAS_MAP")
	if [ -z "$recip" ]; then
		logger -sp mail.warning -t "$progname" \
			'Unable to determine alias destination for recipient.'
		exit $EX_TEMPFAIL
	fi

	if [ -z "$recipients" ]; then
		recipients=$recip
	else
		recipients="$recipients,$recip"
	fi
done

if ! tmpfile=$(mktemp "/tmp/$progname.XXXXXXXXXX"); then
	logger -sp mail.warning -t "$progname" \
		'Unable to create temporary file.'
	exit $EX_TEMPFAIL
fi

# Clean up when done or aborting.
trap 'rm -f "$tmpfile"' EXIT TERM

spamc -U /var/run/spamd -Exu "$SPAMC_USER" >"$tmpfile"
status=$?

case $status in
0)
	formail <"$tmpfile" \
		-A "Delivered-To: $1" | \
		sendmail -if "$sender" "$recipients"
	exit
	;;
1)
	if [ -z "$SPAM_RECIP" ]; then
		# Drop spam on the floor if there's no spam recipient.
		from=$(formail -cx From: <"$tmpfile")
		to=$(formail -cx To: <"$tmpfile")
		logger -sp mail.warning -t "$progname" \
			"Dropping spam message from ${from# } to ${to# }."
		exit 0
	fi

	mail -s "$progname spam" "$SPAM_RECIP" <"$tmpfile"
	exit
	;;
*)
	logger -sp mail.warning -t "$progname" \
		"Temporary SpamAssassin failure (spamc returned $status)"
	exit $EX_TEMPFAIL
	;;
esac