MailFilter

Mail and Spam filtering using the Kinguard Project Installation.

Today a lot of mail that comes into a mailbox is in dire need of filtering. This can be due to spam or just having multiple email addresses landing in the same account that needs to be sorted in different folders depending on the receiver address.

This is work in progress trying to add this functionality to the Kinguard Project software.

Step one: Add spam detection

Spamassassin is a software very commonly used to detect spam. Using ssh to log in to your device it can be installed by:

apt update
apt install spamassasin

Edit /etc/postfix.cf, under the smtp line (~line 12) add "-o content_filter=spamassasin" as below

smtp      inet  n       -       y       -       -       smtpd
  -o content_filter=spamassassin

Next in the same file under the "submission" add the same line:

submission inet n       -       -       -       -       smtpd
  -o syslog_name=postfix/submission
  -o smtpd_tls_security_level=encrypt
  -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
  -o content_filter=spamassassin

Restart postfix

systemctl restart postfix

Step two: Mail filtering

Dovecot is already setup on the device and we need to add support for Seive. This is done uing Pigeonhole (the name is very good, well worth reading the leading paragraph on the project page). This is installed by:

apt install dovecot-sieve dovecot-managesieved dovecot-lmtpd

Edit /etc/dovecot/conf.d/10-master.conf (uncomment/edit as below)

service lmtp {
 unix_listener /var/spool/postfix/private/dovecot-lmtp {
  group = postfix
  mode = 0600
  user = postfix
 }
}

Edit /etc/dovecot/conf.d/10-master.conf and change the "mail_location" parameter

mail_location = maildir:/var/opi/mail/data/%n/mail 

Edit the file /etc/dovecot/conf.d/90-sieve.conf, commenting out the existing sieve line

 # sieve = file:~/sieve;active=~/.dovecot.sieve
 sieve = /var/opi/mail/data/%n/sieve/dovecot.sieve
 sieve_dir = /var/opi/mail/data/%n/sieve

Edit /etc/dovecot/conf.d/20-managesieve.conf, enable services below by uncommenting them.

service managesieve-login {
 inet_listener sieve {
   port = 4190
 }
 inet_listener sieve_deprecated {
   port = 2000
 }

 # Number of connections to handle before starting a new process. Typically
 # the only useful values are 0 (unlimited) or 1. 1 is more secure, but 0
 # is faster. <doc/wiki/LoginProcess.txt>
 service_count = 1

 # Number of processes to always keep waiting for more connections.
 process_min_avail = 0

 # If you set service_count=0, you probably need to grow this.
 vsz_limit = 64M
}

service managesieve {
 # Max. number of ManageSieve processes (connections)
 process_limit = 1024
}

Create /etc/dovecot/conf.d/20-lmtp.conf

protocol lmtp {
 postmaster_address = admin@localhost
 mail_plugins = $mail_plugins sieve
}

Edit /usr/share/roundcube/config/config.inc.php

$config['plugins'] = array(
   'archive',
   'opi_addressbook',
   'opi_identities',
   'zipdownload',
   'managesieve',
);

and adding to the same file

$config['managesieve_host'] = 'localhost';

Edit /etc/postfix/main.cf and at the end add the line

virtual_transport = lmtp:unix:private/dovecot-lmtp

Restart services

systemctl restart dovecot
systemctl restart postfix

Global filtering

If you want to have filters that are executed for all users try the following

Create a location for global scripts

mkdir /etc/kinguard/sieve.d

To be able to run then before and/or after user's personal filters create additional folders

mkdir /etc/kinguard/sieve.d/before
mkdir /etc/kinguard/sieve.d/after

Create scritps in the appropriate sub folder, this is a filter for mail marked as spam by spamassasin Create /etc/kinguard/sieve.d/before/10-junk.sieve

require ["fileinto", "mailbox"];
if header :contains "X-Spam-Flag" "YES" {
   fileinto :create "Junk";
}

The script needs to be compiled since this can not be done run-time by dovecot as it does not have permissions here

cd /etc/kinguard/sieve.d/before
sievec 10-junk.sieve

Add the locations to /etc/dovecot/conf.d/90-sieve.conf

 sieve_before = /etc/kinguard/sieve.d/before
 sieve_after = /etc/kinguard/sieve.d/after

Restart dovecot

systemctl restart dovecot

Debugging

To get some additional information on what is going on, enable mail_debug in /etc/dovecot/conf.d/10-logging.conf

mail_debug = yes

"tail -f /var/log/mail.log" is your friend here.

Exemple Filters

Examples

Useful links

Filter tester Small FAQ