This assumes that you have postfix installed and running as your SMTP server
First, make sure that you’re root
whoami
I probably shouldn’t have to explain that if you’re reading this but just in case; if that last command returned something else than ‘root’ issue the following command
sudo su
and enter your password
step 1: Let’s install the packages we’re gonna need
apt-get update apt-get install spamassassin spamc
step 2: Now we configure spamassasin
cat /etc/default/spamassassin | sed -e 's#ENABLED=0#ENABLED=1#g' > /etc/default/spamassassin cat /etc/default/spamassassin | sed -e 's#CRON=0#CRON=1#g' > /etc/default/spamassassin cat /etc/spamassassin/local.cf | set -e 's## rewrite_header Subject *****SPAM*****#rewrite_header Subject [*****SPAM*****] > /etc/spamassassin/local.cf
and we start/restart it
/etc/init.d/spamassassin restart
step 3: We create a little script that will take desired action upon spamassassin flagging
create a user called spamassassin (or whatever you want as long as you keep it consistent)
useradd -m spamassassin
then edit the script file /home/spamassassin/spamcheck and throw the following in it
# variables
SENDMAIL="/usr/sbin/sendmail -i"
EGREP=/bin/egrep
SPAMLIMIT=10
# exit codes from <sysexits.h>
EX_UNAVAILABLE=69
# clean up when done or when aborting.
trap "rm -f /tmp/out.$$" 0 1 2 3 15
# pipe message to spamc
cat | /usr/bin/spamc -u spamd > /tmp/out.$$
# are there more than $SPAMLIMIT stars in X-Spam-Level header? :
if $EGREP -q "^X-Spam-Level: *{$SPAMLIMIT,}" < /tmp/out.$$
then
# option 1: move spam messages to sideline dir so a human can look at them later:
mv /tmp/out.$$ /home/spamassassin/`date +%Y-%m-%d_%R`-$$
# option 2: divert spam message to an alternate e-mail address:
#$SENDMAIL xyz@xxxx.xx < /tmp/out.$$
# option 3: just delete the spam message
# rm -f /tmp/out.$$
# option 4: still relay the email to the recipient with the subject of the email now containing [*****SPAM*****]
# $SENDMAIL "$@" < /tmp/out.$$
else
$SENDMAIL "$@" < /tmp/out.$$
fi
# Postfix returns the exit status of the Postfix sendmail command.
exit $?
make sure that you
chown spamassassin:spamassassin /home/spamassassin/spamcheck chmod 750 /home/spamassassin/spamcheck
step 4: Ok, so we got spamassassin going and a little script that will take an email and throw it in /home/spamassassin if it’s spam (if you chose option1) now we just need to tell postfix to pass all messages to that script
edit /etc/postfix/master.cf and replace
smtp inet n - - - - smtpd
with
smtp inet n - n - - smtpd -o content_filter=spamcheck:dummy
also add the following 2 lines at the bottom of the file (the indentation is important)
spamcheck unix - n n - 10 pipe
flags=Rq user=spamassassin argv=/bin/spamcheck -f ${sender} -- ${recipient}
We’re almost there, just restart postfix and you’re good to go!
/etc/init.d/postfix restart
If you wanna test that out, watch the log while you send emails to your servers
tail -f /var/log/syslog
send a clean mail, make sure that it reaches destination, then send something you know will get flagged as spam and make sure it ends up in /home/spamassasin instead of the intended recipient.
The reason we choose option 1 here is because there’s no point in still relaying a flagged email as it will still clog the recipient’s mailbox. On the other hand we don’t want to just delete it if spamassassin makes a mistake we want to play it safe and keep every emails should something arise, we quarantine the bad ones in /home/spamassassin
Lastly, as long as you have postfix just feeding the emails to a script like we just did, it’s easy to become fancier and do all kinds of processing to the email, on my server I actually call a php script that throws emails in a DB.