Blok Spam Menggunakan Postfix dan Bogofilter
Disini akan di terangkan cara menggunakan bogofilter untuk mem-filter e-mail yang melalui postfix.
Teori
Kita akan mensetup bogofilter di mail server dan akan mem-filter semua mail yang masuk. Ada beberapa keuntungan yang akan di peroleh karena hal tersebut, yaitu:
- Pengguna e-mail non-unix / non-linux akan memperoleh keuntungan dari bogofilter.
- Bogofilter akan belajar banyak karena akan memperoleh akses ke corpus yang sangat besar.
Di samping itu, juga ada mekanisme bagi pengguna untuk mendaftarkan message spam baru / non-spam termasuk memperbaiki klasifikasi yang salah.
Asumsi
- Langkah yang di terangkan disini membutuhkan privilege sebagai root.
- Postfix di install di /usr. Jika kita menginstall dari repo kemungkinan akan berada disitu. Kalau kita menginstall menggunakan source code maka kemungkinan akan ada di /usr/local/
- Bogofilter di install di /usr/bin/bogofilter di mail server.
Instalasi
instalasi postfix
apt-get install postfix
instalsi bogofilter
apt-get install bogofilter
beri training bogofilter
bogofilter -d . -s < spam.mbx bogofilter -d . -n < nonspam.mbx
Melakukan Filter
- Buat script untuk menjalankan bogofilter, misalnya /usr/local/bin/postfix-filter.sh yang berisi
vi /usr/local/bin/postfix-filter.sh
#!/bin/sh FILTER=/usr/bin/bogofilter FILTER_DIR=/var/spool/filter # WARNING! The -i is crucial, else you may see # messages truncated at the first period that is alone on a line # (which can happen with several kinds of messages, particularly # quoted-printable) # -G is ignored before Postfix 2.3 and tells it that the message # does not originate on the local system (Gateway submission), # so Postfix avoids some of the local expansions that can leave # misleading traces in headers, such as local address # canonicalizations. POSTFIX="/usr/sbin/sendmail -G -i" export BOGOFILTER_DIR=/home/bogofilter # Exit codes from <sysexits.h> EX_TEMPFAIL=75 EX_UNAVAILABLE=69 cd $FILTER_DIR || \ { echo $FILTER_DIR does not exist; exit $EX_TEMPFAIL; } # Clean up when done or when aborting. trap "rm -f msg.$$ ; exit $EX_TEMPFAIL" 0 1 2 3 15 # bogofilter -e returns: 0 for OK, nonzero for error rm -f msg.$$ || exit $EX_TEMPFAIL $FILTER -p -u -e > msg.$$ || exit $EX_TEMPFAIL exec <msg.$$ || exit $EX_TEMPFAIL rm -f msg.$$ # safe, we hold the file descriptor exec $POSTFIX "$@" exit $EX_TEMPFAIL
- Set supaya script bisa di jalankan!
Make sure the script is executable!
Given a good initial corpus, it is better to have bogofilter update its lists based on the message classification, since it is quite likely to get it right. Misclassifications MUST be corrected later.
- Modify your /etc/postfix/master.cf to run the filter.
After the line that starts "smtp " and ends in "smtpd" (don't confuse it with the one that ends in "smtp", mind the "d"!) and add the following line, you must indent it with some spaces or tabs:
-o content_filter=filter:
At the end of the file, add the following two lines:
filter unix - n n - - pipe flags=Rq user=filter argv=/home/bogofilter/postfix-filter.sh -f ${sender} -- ${recipient}
- Now, every incoming message will have the header line
X-Bogosity: ...
added to the headers. A bogofilter classified spam messages will have the entry:
X-Bogosity: Spam ...
Note that the actual header name is configurable at compile time and may have been changed.
- Educate your users on how to filter their spam based on the value of
the X-Bogosity header. Spam messages should be diverted to a spam mailbox, rather than deleted.
Registration and Correction:
To use external filtering with Postfix, create a Unix group on the server named "filter".
Next, create a user account named "filter" on the server and make it a member of group "filter". This will be a least-privileged account used by the scripts.
No other user should belong to group "filter". Logins for the "filter" account should be locked (e. g. 'passwd -l filter' on Linux and Solaris) and the shell in /etc/passwd should be set to an invalid shell such as /bin/false.
Arrange for users to send misclassified mail to a particular mailbox and make sure that the database is updated regularly.
If you cannot arrange for regular corrections, remove the "-u" from the bogofilter command in the script above, and update the database as the need arises by registering more mail.
- Make sure the script is executable
# chmod +x /home/bogofilter/postfix-filter.sh
- Change the ownership of /home/bogofilter to the filter user
# chown -R filter:filter /home/bogofilter
- Done!
Author:
David Relson <relson@osagesoftware.com> Matthias Andree <matthias.andree@gmx.de>