How to Install SpamAssassin with Postfix on Ubuntu

SpamAssassin is an open-source mail filter that identifies spam emails using a wide range of heuristic tests. This guide explains how to install SpamAssassin on Ubuntu 20.04 LTS or 21.04.

Prerequisites

• Deploy an Ubuntu cloud server instance at Vultr.
• Install Postfix mail transfer agent.
• Create a sudo user.
• Verify the server has outbound port 25 open.

1. Install SpamAssassin

1. Connect to your server with SSH.

2. Install SpamAssassin.

    $ sudo apt-get update
    $ sudo apt-get install spamassassin spamc -y

3. Add a SpamAssassin user and disable the login.

    $ sudo adduser spamd --disabled-login

2. Configure SpamAssassin

Assign the spamd user account to SpamAssassin and set the log and default home directories.

1. Edit the configuration settings.

    $ sudo nano /etc/default/spamassassin

2. Find the line:

    ENABLED=1

   Uncomment it by removing # and change the value from 1 to 0.

    ENABLED=0

3. Find the line:

    OPTIONS="--create-prefs --max-children 5 --helper-home-dir"

   Change it to include the SpamAssassin user account and log files directory.

    OPTIONS="--create-prefs --max-children 5 --username spamd --helper-home-dir /home/spamd/ -s /home/spamd/spamd.log"

4. Find the line:

    CRON=0

   Change the value from 0 to 1.

    CRON=1

5. Save and close the file.

6. Make a backup of the SpamAssassin local configuration file.

    $ sudo mv /etc/spamassassin/local.cf  /etc/spamassassin/local.cf.bk

7. Create a new SpamAssassin local configuration file.

    $ sudo nano /etc/spamassassin/local.cf 

8. Paste the information below to the file.

    rewrite_header Subject ***** SPAM _SCORE_ *****
    report_safe             0
    required_score          5.0
    use_bayes               1
    use_bayes_rules         1
    bayes_auto_learn        1
    skip_rbl_checks         0
    use_razor2              0
    use_dcc                 0
    use_pyzor               0
    ifplugin Mail::SpamAssassin::Plugin::Shortcircuit
    endif

9. Save and close the file.

3. Configure Postfix

1. Edit your Postfix configuration file.

    $ sudo nano /etc/postfix/master.cf

2. Locate these entries.

    smtp      inet  n       -       y       -       -       smtpd
    #smtp      inet  n       -       y       -       1       postscreen
    #smtpd     pass  -       -       y       -       -       smtpd
    #dnsblog   unix  -       -       y       -       0       dnsblog
    #tlsproxy  unix  -       -       y       -       0       tlsproxy
    submission inet n       -       y       -       -       smtpd

3. Below the smtp configuration, add a SpamAssassin content filter.

    smtp      inet  n       -       y       -       -       smtpd
   
    -o content_filter=spamassassin
    spamassassin unix -     n       n       -       -       pipe
    user=spamd argv=/usr/bin/spamc -f -e  
    /usr/sbin/sendmail -oi -f ${sender} ${recipient}

4. Save and close the file.

5. Restart Postfix and enable SpamAssassin to run at system startup.

    $ sudo systemctl restart postfix.service
    $ sudo systemctl enable spamassassin.service
    $ sudo systemctl start spamassassin.service 

More Information

To learn more about SpamAssassin, please see the official website.