anti-spam filter used by the FreeBSD mailing lists.

etc/mail/Makefile

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+default:
+.if exists(/etc/mail/ips.txt)
+	mv -f /etc/mail/ips.txt /etc/mail/ips.txt.0
+.endif
+	fetch ftp://ftp.gulf.net/pub/docs/ips.txt
+	cat /etc/mail/ips.txt | cut -d ' ' -f 1 | \
+		sed -e 's/$$/ 	#blocked. contact postmaster/' > \
+		/etc/mail/ips.new
+	mv /etc/mail/ips.new /etc/mail/ips.txt
+.if exists(/etc/mail/domains.txt)
+	mv -f /etc/mail/domains.txt /etc/mail/domains.txt.0
+.endif
+	fetch ftp://ftp.gulf.net/pub/docs/domains.txt
+	cat /etc/mail/domains.txt | cut -d ' ' -f 1 | \
+		sed -e 's/$$/ 	#blocked. contact postmaster/' > \
+		/etc/mail/domains.new
+	mv /etc/mail/domains.new /etc/mail/domains.txt
+
+install:
+	makemap hash /etc/mail/spamsites < /etc/mail/domains.txt
+.if exists(/etc/mail/spamsites.local)
+	makemap -o hash /etc/mail/spamsites < /etc/mail/spamsites.local
+.endif
+	makemap hash /etc/mail/denyip < /etc/mail/ips.txt
+.if exists(/etc/mail/denyip.local)
+	makemap -o hash /etc/mail/denyip < /etc/mail/denyip.local
+.endif
+
+all: default install

etc/mail/README

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+	Filtering out SPAM from your site
+
+Introduction:
+	The FreeBSD Project filters spam, unsolicited commerical
+e-mail, from its mailing lists.  The filter has two parts: databases
+and rulesets.  We have added three rulesets to /etc/sendmail.cf,
+check_relay and check_mail and xlat. (xlat is for testing only, as
+explained in /etc/mail/sendmail.cf.additions.) These rulesets use
+two databases.  The denyip, a list of IP addresses, and spamsites,
+a list of domains.  We do not accept mail from any machine that
+matches a entry in either database.
+
+Filtering at your site:
+	To filter spam at your site you need to:
+	1. modify your /etc/sendmail.cf, 
+	2. retrieve the database source files from the master site,
+	3. make the databases and 
+	4. finally signal sendmail that the configuration file has changed.
+
+1. Modifying your /etc/sendmail.cf
+	Add the database declarations and the rulesets contained
+in /etc/mail/sendmail.cf.additions to your .mc file.  If you do
+not use m4 to generate your /etc/sendmail.cf, add the database
+declarations to your /etc/sendmail.cf.
+
+2. Fetching the database source files:
+	The database source files are available from Gulf Coast
+Internet via anonymous FTP.  The Makefile in /etc/mail will retreive
+the source files for you: as root, type "cd /etc/mail; make" at
+the command line.  The previous version of the database source
+files is moved to <filename>.0.  Local additions should be kept in
+separate files.  We use spamsites.local and denyip.local.  You may
+want to diff the new versions of the files against the previous
+versions to see what has changed.
+
+3. Make the databases:
+	As root, type "cd /etc/mail; make install" will build the
+two databases from the retrieved source files and the local additions
+files.
+
+4. Signaling sendmail:
+	Sendmail will reread its configuration whenever sendmail
+receives a HUP signal.  As root, type "kill -HUP `cat
+/var/run/sendmail.pid`".  Check sendmail's log file to be sure that
+it has restarted.  /var/log/maillog should contain the line:  "Oct
+15 08:59:16 hub sendmail[6565]: restarting /usr/sbin/sendmail on
+signal".  Most likely, the date, time, hostname and process id will
+be differ.
+
+Testing the spam filter:
+
+How can I tell if its working:
+	The mail log file, /var/log/maillog, will contain a line
+for every message filtered.  The lines will be similar to one of
+these two log entries:
+
+Check_mail rejects:
+"Oct 15 02:43:26 hub sendmail[6565]: CAA06565: ruleset=check_mail,
+arg1=<announce@martianconsulate.com>, relay=xxx.isp.net [###.###.###.###],
+reject=521 <announce@martianconsulate.com>"
+
+Check_relay rejects:
+Oct 19 04:45:24 hub sendmail[3503]: NOQUEUE: ruleset=check_relay,
+arg1=imsp015.netvigator.com, arg2=205.252.144.206, relay=root@localhost,
+reject=521 blocked.contact postmaster@FreeBSD.ORG

etc/mail/sendmail.cf.additions

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+# database declarations
+Kdenyip hash -o -a.REJECT /etc/mail/denyip.db
+Kspamsites hash -o -a.REJECT /etc/mail/spamsites.db
+
+# called with host.tld and IP address of connecting host.
+# ip address must NOT be in the "denyip" database
+Scheck_relay
+R$* $| [$+		$1 $| $2			should not be needed
+R$* $| $+]		$1 $| $2			same (bat 2nd ed p510)
+R$* $| $*		$: $1 $| $(denyip $2 $)
+R$* $| $*.REJECT	$#error $: 521 blocked. contact postmaster@FreeBSD.ORG ($2)
+# host must *not* be in the "spamsites" database
+R$+.$+.$+ $| $*		$2.$3 $| $4
+R$+.$+ $| $*		$: $(spamsites $1.$2 $) $| $3
+R$*.REJECT $| $*	$#error $: 521 blocked. contact postmaster@FreeBSD.ORG ($1)
+# Host must be resolvable, currently not used at hub.freebsd.org
+#R$* $| $*		$: <?> <$1 $| $2> $>3 foo@$1
+#R<?> <$*> $*<@$*.>	$: $1
+#R<?> <$*> $*<@$*>	$#error $: 451 Domain does not resolve ($1)
+
+# called with envelope sender, "Mail From: xxx", of SMTP conversation
+#
+Scheck_mail
+R$*			$: <?> $>3 $1
+R<?> $* < @ $+ . >	$: $2 
+# R<?> $* < @ $+ >	$#error $: "451 Domain does not resolve"
+R<?> $* < @ $+ >	$: $2
+R$+.$+.$+		$2.$3  
+R$*			$: $(spamsites $1 $: OK $)
+ROK			$@ OK 
+R$+.REJECT		$#error $: 521 $1 
+
+# for testing check_relay and check_mail
+# if we type "$|", sendmail will split this into two tokens "$" and "|"
+# this rule glues prevent sendmail from splitting "$|"
+# to use:  /usr/sbin/sendmail -bt
+#          host.domain.tld $| 111.222.333.444
+Sxlat
+R$* $$| $*		$: $1 $| $2
+R$* $| $*		$@ $>check_relay $1 $| $2