Spamassassin Filter Customized Per User With Automatic SPAM Learning


After obvious spam has been rejected before queuing using the Spamass-Milter, we can now proceed to check for spam specifically for each user. The automation is based on each mail account having a Junk folder in its top directory - just as most mail clients already prepare at first start. Note that the name of the folder is case-sensitive and you need the capital ‘J’ if you use the following scripts and configuration entries.

First of all, we need to maintain a separate spam database for each mail account. I create a directory tree and populate the bayes database using the following script, saved as inside /etc/cron.daily.

# script to create a directory under /vhome/users for each mail account,
# populate the spam db with sa-learn, and fix the dir's permissions.

# get all mail accounts
for dir in /var/spool/postfix/virtual/*; do
  echo "creating dir for $mailaccount"
  mkdir -p ${spamdbpath}

  if [ -d ${junkfolder} ]; then
    echo "learning spam from ${junkfolder} for user ${mailaccount}"
    sa-learn --spam --dbpath ${spamdbpath}/bayes --progress ${junkfolder}
    sa-learn --sync
    echo "no Junk folder in top level - skipping"

  if [ -d ${hamfolder} ]; then
    echo "learning ham from ${hamfolder} for user ${mailaccount}"
    sa-learn --ham --dbpath ${spamdbpath}/bayes --progress ${hamfolder}
    sa-learn --sync
    echo "no Archive folder in top level - skipping"

echo "fix permissions for whole vhome"
chown -R vmail:mail /vhome
chmod -R 700 /vhome

This script is automatically run every day, which should be frequent enough for most purposes.

Then, we need to configure spamd, which is done in the file /etc/default/spamassassin. I simply change the OPTIONS variable to the following line.

OPTIONS="--create-prefs --max-children 5 --helper-home-dir --virtual-config-dir=/vhome/users/%u/spamassassin -x -u vmail"

The option virtual-config-dir tells spamd to check for user databases in the virtual home directory tree instead of real user home directories. The x and u options are mandatory for setting the virtual-config-dir and I set them to the appropriate values.

Now we need to tell postfix to use spamc and specify the name of the mail account for spamc invokation. Therefore, I change the delivery agent line in /etc/postfix/ to:

# Dovecot LDA
dovecot   unix  -       n       n       -       -       pipe
  flags=DRhu user=vmail:mail argv=/usr/bin/spamc -u ${recipient} -e /usr/lib/dovecot/deliver -f ${sender} -d ${recipient}

Then don’t forget to reload spamassassin, dovecot and postfix to enable the changes to the configuration files:

/etc/init.d/spamassassin restart
/etc/init.d/dovecot restart
/etc/init.d/postfix restart

That’s it again :)
If you are unsure whether your setup really works, you should check the log using tail -f /var/log/ and send yourself a message.