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

Connect to your server with SSH.
Install SpamAssassin.$ sudo apt-get update $ sudo apt-get install spamassassin spamc -y
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.

Edit the configuration settings.$ sudo nano /etc/default/spamassassin
Find the line:ENABLED=1 Uncomment it by removing # and change the value from 1 to 0.ENABLED=0
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"
Find the line:CRON=0 Change the value from 0 to 1.CRON=1
Save and close the file.
Make a backup of the SpamAssassin local configuration file.$ sudo mv /etc/spamassassin/local.cf /etc/spamassassin/local.cf.bk
Create a new SpamAssassin local configuration file.$ sudo nano /etc/spamassassin/local.cf
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
Save and close the file.

3. Configure Postfix

Edit your Postfix configuration file.$ sudo nano /etc/postfix/master.cf
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
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} ${recipient}
Save and close the file.
Restart Postfix and enable SpamAssassin to run at system startup.$ 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.

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