#!/usr/bin/perl -w

# Spamassassin filter for POP3 mail accounts

# Copyright (C) 2003 Nigel Horne, Wharfedale Computers Ltd.
# njh@despammed.com
# 21/11/02:	Use DNS to check originating host exists to help stop spam
# 22/11/02:	Use MX DNS records.
# 25/11/02:	Flush items put in sendmail's queue.
# 2/12/02:	Handle e-mail addresses without the realname
# 21/1/03:	Added spam blocker
# 22/1/03:	Don't forward spam message. Improved spam warning messages
# 24/1/03:	Added virus checker.

use strict;
use Net::POP3;
use Net::DNS;
use Mail::SpamAssassin;

my $hostname = 'smsltd.demon.co.uk';
my $server = 'pop3.demon.co.uk';
my $user = 'smsltd';
my $password = 'xyzzy';

my $pop3 = Net::POP3->new($server, Timeout => 60) or
	die "Cannot connect to $server: $!";

my $nummessages = $pop3->login($user, $password);

if(!defined $nummessages) {
	die "Cannot login to $server: $!";
}

if($nummessages == 0) {
	print "Nothing to do\n";
	$pop3->quit();
	exit 0;
}

print "Retrieving $nummessages messages from $server\n";

my $messages = $pop3->list() or
	die "Cannot get list of messages from $server: $!";

my $resolver = Net::DNS::Resolver->new;

sub CATCH_PIPE { };
$SIG{'PIPE'} = "CATCH_PIPE";

MESSAGE: foreach my $msgid (keys %$messages) {
	print "Forwarding message $msgid ...";

	my $message = $pop3->get($msgid);

	defined $message or die "\nCan't retrieve message $msgid: $!";

	print "\n";

	my $from = "";

	my @messageArray = @$message;

	foreach (@messageArray) {
		if(/^From: (.+)/) {
			$from = $1;
			if(($from =~ /.*\<.+\@(.+)\>/) ||
			   ($from =~ /.+\@(.+)/)) {
				unless(mx($resolver, $1)) {
					print "Unknown host $1 in $from, message not forwarded\n";
					# You may wish to comment this out
					$pop3->delete($msgid);
					next MESSAGE;
				}
			} else {
				$from = 'unknown';
			}
			last;
		}
	}

	if(open(CLAM, "|clamscan --disable-summary -i --mbox -")) {
		print CLAM "From $from\n";

		foreach (@messageArray) {
			print CLAM $_;
		}

		if(close CLAM != 0) {
			if(($from ne "") && open(MAIL, "|/usr/lib/sendmail \"-f$from\" -t -odq")) {
				print MAIL "From MAILER-DAEMON\n";
				print MAIL "To: $from\n";
				print MAIL "Cc: postmaster\n";
				print MAIL "Subject: Virus intercepted\n\n";

				print MAIL "A message sent from you contained a virus.\n";
				print MAIL "It has not been forwarded to the $hostname domain.\n";
				close MAIL;
			}
			print "Not forwarding message containing a virus\n";
			# You may wish to comment this out
			$pop3->delete($msgid);
			next MESSAGE;
		}
	}

	my $ma = Mail::SpamAssassin::NoMailAudit->new(data => \@messageArray);

	# This often gives this error:
	#	Use of uninitialized value in split at /usr/lib/perl5/5.8.0/File/Spec/Unix.pm line 216
	my $sa = Mail::SpamAssassin->new;
	my $status = $sa->check($ma);

	if($status->is_spam()) {
		$status->rewrite_mail();

		# Don't report if the from is forged as us, or if it's a bounce
		# of a bounce
		my $isbounce = 0;
		foreach (@messageArray) {
			if(/^From: (.+)\@$hostname(.*)/) {
				$isbounce = 1;
				last;
			}
		}
		$sa->report_as_spam($ma) unless $isbounce;

		print "Not forwarding spam message\n";
		# You may wish to comment this out...
		$pop3->delete($msgid);

		$status->finish();

		next MESSAGE;
	}

	$status->finish();
	undef $status;
	undef $sa;
	undef $ma;

	# If we're here it probably isn't spam
	if($from eq "") {
		$from = 'unknown';
	} elsif(open(MAIL, "|/usr/lib/sendmail \"-f$from\" -t -odq")) {
		print MAIL "From njh\@despammed.com\n";
		print MAIL "To: $from\n";
		print MAIL "From: Nigel Horne <njh\@despammed.com>\n";
		print MAIL "Subject: Please update your address book\n\n";

		print MAIL "This is an automatic message that has been sent\n";
		print MAIL "in response to a message sent to $hostname.\n\n";
		print MAIL "The domain $hostname is about to disappear.\n";
		print MAIL "Please update your address book to point to bandsman.co.uk.\n";
		close MAIL;
	}

	if(open(MAIL, "|/usr/lib/sendmail \"-f$from\" -t")) {
		# Send TO field first
		foreach (@$message) {
			if(/^To: (.+)\@$hostname(.*)/i) {
				print MAIL "To: $1$2\n";
				print "To: $1$2\n";
				last;
			} elsif (/^To: (.+)/i) {
				print MAIL "To: $1\n";
				print "To: $1\n";
				last;
			} elsif (/^$/) {
				# End of headers. No To: found. Must be spam...
				print "Not forwarding spam message\n";
				$pop3->delete($msgid);

				close MAIL;

				next MESSAGE;
			}
		}
		my $inhead = 1;
		foreach (@$message) {
			if($inhead) {
				(/^From: (.+)/) && print "From: $1\n";
				(/^Subject: (.+)/) && print "Subject: $1\n";

				unless (/^To: .+\@$hostname.*/) {
					print MAIL $_ || die "Sendmail has disappeared: $!\n";
				}
				$inhead = 0 if(/^$/);
			} else {
				print MAIL $_ || die "Sendmail has disappeared: $!\n";
			}
		}

		print MAIL "\nForwarded from the pop3 account at $server.";
		print MAIL "\nThis service will terminate soon. You *have* been warned.\n";

		if(close MAIL) {
			$pop3->delete($msgid);
		} else {
			warn "e-mail may have failed\n";
			# You may wish to comment this out...
			$pop3->delete($msgid);
		}
	}
}

print "Finished\n";

$pop3->quit();