This assumes that you have postfix installed and running as your SMTP server
First, make sure that you’re root
1 | 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
1 | sudo su |
and enter your password
step 1: Let’s install the packages we’re gonna need
1 2 | apt-get updateapt-get install spamassassin spamc |
step 2: Now we configure spamassasin
1 2 3 | cat /etc/default/spamassassin | sed -e 's#ENABLED=0#ENABLED=1#g' > /etc/default/spamassassincat /etc/default/spamassassin | sed -e 's#CRON=0#CRON=1#g' > /etc/default/spamassassincat /etc/spamassassin/local.cf | set -e 's## rewrite_header Subject *****SPAM*****#rewrite_header Subject [*****SPAM*****] > /etc/spamassassin/local.cf |
and we start/restart it
1 | /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)
1 | useradd -m spamassassin |
then edit the script file /home/spamassassin/spamcheck and throw the following in it
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 | # 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
1 2 | chown spamassassin:spamassassin /home/spamassassin/spamcheckchmod 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
1 | smtp inet n - - - - smtpd |
with
1 | 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)
1 2 3 | spamcheck unix - n n - 10 pipeflags=Rq user=spamassassin argv=/bin/spamcheck -f ${sender} -- ${recipient} |
We’re almost there, just restart postfix and you’re good to go!
1 | /etc/init.d/postfix restart |
If you wanna test that out, watch the log while you send emails to your servers
1 | 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.
