Install SpamAssassin and MIMEDefang need a lots of optional package, you can get it from http://search.cpan.org

1. Install SpamAssassin

# groupadd spamd
# useradd -g spamd -s /bin/false spamd
# tar xzvf Mail-SpamAssassin-3.0.2.tar.gz
# cd Mail-SpamAssassin-3.0.2
# export LC_ALL=C
# perl Makefile.PL
# make
# make install
# cp spamd/redhat-rc-script.sh /etc/rc.d/init.d/spamd
# chmod 755 /etc/rc.d/init.d/spamd
# chkconfig --add spamd
# vi /etc/rc.d/init.d/spamd

SPAMDOPTIONS="-d -c -u spamd -H /home/spamd -m5"

# vi /etc/mail/spamassassin/local.cf (my local.cf)

# These values can be overridden by editing ~/.spamassassin/user_prefs.cf
# (see spamassassin(1) for details)

# These should be safe assumptions and allow for simple visual sifting
# without risking lost emails.

required_hits 5.5
rewrite_subject 1
rewrite_header Subject *****SPAM*****
report_safe 1
defang_mime 0
rewrite_subject 1
report_header 1
use_terse_report 1
whitelist_from *@quickmail.51job.com
whitelist_from *@gmail.com
#whitelist_from *@163.com
whitelist_from *@sina.com
whitelist_from *@126.com
whitelist_from *@21cn.com
whitelist_from *@qq.com
whitelist_from *@tom.com
whitelist_from *@yahoo.com.cn
whitelist_from *@hotmail.com
whitelist_from *@sky.net.cn
whitelist_from *@gddc.com.cn
whitelist_from *@sharebank.com.cn
whitelist_from *@pcsoft.com.cn
whitelist_from *@igrand.cn
whitelist_from *@iresearch.cn

use_bayes 1
auto_learn 1
skip_rbl_checks 1
use_razor2 0
use_dcc 0
use_pyzor 0

score SUBJ_FULL_OF_8BITS 0.0
score BASE64_ENC_TEXT 0.0
score BAYES_99 0.1
score BAYES_90 0.1
score BAYES_80 0.1
score BAYES_70 0.1
score BAYES_60 0.1
score FROM_ILLEGAL_CHARS 0.1
score HEAD_ILLEGAL_CHARS 0.1
score SUBJ_ILLEGAL_CHARS 0.1
score MIME_BASE64_TEXT 0.1
score FAKE_HELO_AOL 0.1
score NO_RDNS_DOTCOM_HELO 0.1
score MIME_HTML_ONLY 0.1
score SUBJ_HAS_UNIQ_ID 0.1
score HTML_SHORT_COMMENT 0.5
score MISSING_SUBJECT 0.1
score RCVD_DOUBLE_IP_SPAM 2.0

score BAYES_99 0 0 2.700 2.000
score BAYES_50 0.2
score BAYES_56 0.2
score ADDR_NUMS_AT_BIGSITE 0.522 0.362 .543 0.699
score FROM_ENDS_IN_NUMS 0.999 0.869 0.677 0.594
score FROM_WEBMAIL_END_NUMS6 0.489 1.062 0.809 1.399
score FROM_NUM_AT_WEBMAIL 0.506 0.501 2.100 2.100
score HTML_20_30 0.691 0.474 1.572 1
score HTML_30_40 0.837 0.809 1.919 1
score HTML_40_50 0.870 0.474 1.898 1
score HTML_50_60 0.699 0.183 1.514 2.100
score HTML_60_70 0.359 0.100 1.516 2.113
score HTML_70_80 0.383 0.105 1.305 2.100
score HTML_80_90 0.014 0 1 1
score HTML_90_100 0.308 1.073 1.5 2.187
score HTML_FONTCOLOR_BLUE 1.100
score HTML_FONT_BIG 0.571 0.500 0.570 0.567
score HTML_MESSAGE 0.5

ok_locales en zh

#Subject is all English
header __EIS_RULE_SUBJECT_WITH_CHN Subject =~ /[\x80-\xff][\x80-\xff]/
meta EIS_RULE_SUBJECT_NO_CHN !__EIS_RULE_SUBJECT_WITH_CHN
describe EIS_RULE_SUBJECT_NO_CHN EIS_RULE_SUBJECT_NO_CHN
score EIS_RULE_SUBJECT_NO_CHN 5

#Content is all English
body __EIS_RULE_BODY_WITH_CHN /[\x80-\xff][\x80-\xff]/
meta EIS_RULE_BODY_NO_CHN !__EIS_RULE_BODY_WITH_CHN
describe EIS_RULE_BODY_NO_CHN EIS_RULE_BODY_NO_CHN
score EIS_RULE_BODY_NO_CHN 3

Make a spam and non-spam test

# spamassassin -t < sample-spam.txt > spamtest.txt
# less spamtest.txt
# spamassassin -t < sample-nonspam.txt > nospamtest.txt
# less nospamtest.txt

"*****SPAM*****" is included in spamtest.txt, not included in nospamtest.txt.

Create SpamAssassin learning system.

# sa-learn --rebuild -D -p user_prefs
# sa-learn --dump all (view learning data)

Edit openwebmail config:

spamcheck_pipe /usr/bin/spamc -c -x -t60 -u @@@USERNAME@@@

2. Install MIME-tools

# wget http://www.mimedefang.org/static/MIME-tools-5.420.tar.gz
# tar xzvf MIME-tools-5.420.tar.gz
# cd MIME-tools-5.420
# perl Makefile.PL
# make
# make install

3. Install MIMEDefang

# wget http://cpan.linuxforum.net/authors/id/D/DS/DSKOLL/IO-stringy-2.110.tar.gz
# wget http://search.cpan.org/CPAN/authors/id/M/MA/MARKOV/MailTools-1.77.tar.gz
# wget http://search.cpan.org/CPAN/authors/id/G/GA/GAAS/MIME-Base64-3.07.tar.gz (These package are needed by my system)
# wget http://www.mimedefang.org/static/mimedefang-2.63.tar.gz
# tar xzvf mimedefang-2.63.tar.gz
# cd mimedefang-2.63
# ./configure
# useradd defang
# make
# make install
# cp examples/init-script /etc/init.d/ (redhat linux is redhat/mimedefang-init)

# vi /etc/mail/sendmail.cf
# Input mail filters
O InputMailFilters=mimedefang

######################################################################
######################################################################
#####
##### MAIL FILTER DEFINITIONS
#####
######################################################################
######################################################################
Xmimedefang, S=unix:/var/spool/MIMEDefang/mimedefang.sock, F=,T=S:60s;R:60s;E:60s

# service sendmail restart
# wget -N -P /usr/share/spamassassin/ www.ccert.edu.cn/spam/sa/Chinese_rules.cf
# vi /etc/init.d/mimedefang-init

MX_USER="defang" #Otherwise it can't be start up.

# vi /etc/procmailrc

# Start up SpamAssassin, filter all incoming mail through SpamAssassin and tags probable spam with a unique header
# Only the email that less than 100K is needed check.
#### Move it to the spam box if it include the letter "Spam"
#SHELL=/bin/sh
LOGFILE=/var/log/procmail.log #Write it to the logs
MAILDIR=/var/mail
VERBOSE=off
PATH=/bin:/sbin:/usr/bin:/usr/sbin/:/usr/local/bin:/usr/local/sbin
LOGFILE=/var/log/procmail.log
:0fw: spamassassin.lock
* < 100000 #
| /usr/bin/spamassassin #Just check the mail that less than 100K

:0:
* ^X-Spam-Flag: Yes
$HOME/mail/spam-mail

# /etc/init.d/spamd start
# /etc/init.d/mimedefang-init start

/etc/init.d/mimedefang-init: line 163: mimedefang.pl: command not found
#BUG FIX FOR REDHAT INIT SCRIPT:
# The configtest procedure in the redhat init script is needs $PROGDIR
# prepended in case mimedefang.pl isn't in the path:

# e.g., line 163 should read:

$PROGDIR/mimedefang.pl $([ -n "$SUBFILTER" ] && echo "-f $SUBFILTER") -test > /var/spool/MIMEDefang/configtest.out 2>&1

Observe statistics of the system log
mailstat -km /var/log/procmail.log

Download the filter file from Chinese Anti-Spam Union regularly:
0 0 1 * * wget -N -P /usr/share/spamassassin http://www.ccert.edu.cn/spam/sa/Chinese_rules.cf;/etc/init.d/mimedefang-init restart