How to set-up server-side email filtering with Dovecot Sieve and Roundcube on a CentOS 6 VPS

The following article is part 6 of the mailserver set-up with virtual users and domains using Postfix and Dovecot series. It covers the steps used to set-up server-side email filtering with Dovecot Sieve and Roundcube on a CentOS 6 VPS

At the end of this article you will end up having the ability to set-up your own server-side mail filter rules and automatically deliver emails to specific maildir based on a filter rule.

What is all this about?

The project behind this is known as Pigeonhole. It’s great because it adds support for the Sieve language (RFC 5228) and the ManageSieve protocol (RFC 5804) to the Dovecot Secure IMAP Server. Additionally, one can easily manage these filter rules via Roundcube’s web interface.

UPDATE THE SYSTEM

Before proceeding any further, make sure you are in a screen session and check if your CentOS Linux VPS is fully up-to-date by running:

## screen -U -S sieve-screen
## yum update

---

ENABLE DOVECOT MANAGE-SIEVE

In order to enable ManageSieve protocol in Dovecot we need to install the dovecot-pigeonhole package using ‘yum’

## yum install dovecot-pigeonhole

Once the package is installed, navigate to dovecot’s configuration directory in /etc/dovecot and edit the main configuration file dovecot.conf

## cd /etc/dovecot
## vim dovecot.conf

set protocols to

protocols = imap lmtp sieve

add auth-master unix-listener to service auth

service auth {
    unix_listener auth-client {
        group = postfix
        mode = 0660
        user = postfix
    }

    unix_listener auth-master {
        group = vmail
        mode = 0660
        user = vmail
    }

    user = root
}

and add the following to the end of the configuration file:

service managesieve-login {
  inet_listener sieve {
    port = 4190
  }
}
service managesieve {
}
protocol sieve {
    managesieve_max_line_length = 65536
    managesieve_implementation_string = dovecot
    log_path = /var/log/dovecot-sieve-errors.log
    info_log_path = /var/log/dovecot-sieve.log
}
plugin {
    sieve = ~/dovecot.sieve
    sieve_global_path = /etc/dovecot/sieve/default.sieve
    sieve_dir = ~/sieve
    sieve_global_dir = /etc/dovecot/sieve/global/
}
lda_mailbox_autocreate = yes
lda_mailbox_autosubscribe = yes
protocol lda {
    mail_plugins = $mail_plugins autocreate sieve quota
    postmaster_address = postmaster@mydomain.com
    hostname = mail.mydomain.com
    auth_socket_path = /var/run/dovecot/auth-master
    log_path = /var/log/dovecot-lda-errors.log
    info_log_path = /var/log/dovecot-lda.log
}
protocol lmtp {
    mail_plugins = $mail_plugins autocreate sieve quota
    log_path = /var/log/dovecot-lmtp-errors.log
    info_log_path = /var/log/dovecot-lmtp.log
}

set-up some necessary stuff

## touch /var/log/{dovecot-lda-errors.log,dovecot-lda.log}
## touch /var/log/{dovecot-sieve-errors.log,dovecot-sieve.log}
## touch /var/log/{dovecot-lmtp-errors.log,dovecot-lmtp.log}
## mkdir -p /etc/dovecot/sieve/global

## chown vmail: -R /etc/dovecot/sieve
## chown vmail:mail /var/log/dovecot-*

restart dovecot for the changes to take effect

## service dovecot restart

verify manage-sieve is exposed on port 4190

## netstat -tunlp | grep :4190

---

SET-UP GLOBAL SPAM FILTERS

Next step is to actually test the server-side filter by setting up a global SPAM sieve filter rule in /etc/dovecot/sieve/default.sieve. This rule should match all emails marked as SPAM by SpamAssassin and move them to the Spam maildir. So, create the following:

## vim /etc/dovecot/sieve/default.sieve

and add the sieve rules below

require ["fileinto"];
# rule:[SPAM]
if header :contains "X-Spam-Flag" "YES" {
        fileinto "Spam";
}
# rule:[SPAM2]
elsif header :matches "Subject" ["*money*","*Viagra*","Cialis"] {
        fileinto "Spam";
}

---

SET-UP POSTFIX DELIVERY

for this to work we need to edit two Postfix configuration files. Start with editing /etc/postfix/main.cf

## vim /etc/postfix/main.cf

and change/add the following

virtual_transport = dovecot
dovecot_destination_recipient_limit = 1

next open /etc/postfix/master.cf and add the following to the end of the file

dovecot   unix  -       n       n       -       -       pipe
  flags=DRhu user=vmail:vmail argv=/usr/libexec/dovecot/deliver -f ${sender} -d ${recipient}

restart postfix for the changes to take effect

## service postfix restart

with all that in place, send an email to some email account on the server using the subject below

XJS*C4JDBQADN1.NSBN3*2IDNEN*GTUBE-STANDARD-ANTI-UBE-TEST-EMAIL*C.34X

the email should be flagged as SPAM by SpamAssassin and moved to the Spam maildir by Dovecot LDA

---

ENABLE SIEVE PLUGIN IN ROUNDCUBE

to be able to manage server-side filter rules through Roundcube, we need to enable the manage-sieve plugin by editing few configuration files.

change to Roundcube’s document root in /var/www/html/roundcube/

## cd /var/www/html/roundcube/

edit Roundcube’s main configuration file and set the following:

## vim +/PLUGINS config/main.inc.php
...
$rcmail_config['plugins'] = array('managesieve');

next, proceed with changing to /var/www/html/roundcube/plugins/managesieve/

## cd plugins/managesieve/

copy the default configuration file and set the following:

## cp config.inc.php.dist config.inc.php
## vim config.inc.php
...
$rcmail_config['managesieve_port'] = 4190;
...
$rcmail_config['managesieve_default'] = '/etc/dovecot/sieve/default.sieve';

now you can login to your Roundcube WebMail, navigate to Settings > Filters and create new filter sets and/or filter rules.

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Implementing server-side email filtering to the mailserver set-up with virtual users and domains using Postfix and Dovecot adds another great and useful feature. Now you can easily filter and organize your emails.

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Of course, if you are one of our Linux VPS Hosting customers, you don’t have to do any of this, simply ask our admins, sit back and relax. Our admins will set this up for you immediately.

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