How to eliminate spam mail using SpamAssassin in Postfix

This article explains how to install SpamAssassin on Postfix on CentOS 7 Linux platform.

Prerequisites

The following conditions have been verified in writing this article.

• CentOS 7.x
• Postfix 2.x
• SpamAssassin 3.x

The Postfix version can be checked with the following method

postconf -d | grep mail_version.

Checking SpamAssassin version

spamassassassin -V.

SpamAssassin installation instructions

$ sudo yum update    
$ sudo yum install spamassassin    

To configure SpamAssassin.

`$ sudo vi /etc/mail/spamassassin/local.cf

In the configuration file, include the following

required_hits 5.0    
report_safe 0    
required_score 5    
rewrite_header Subject [SPAM].    

Create a new user to run SpamAssassin.
Specifically, add the spamd group and create a user without a shell.

$ sudo groupadd spamd    
$ sudo useradd -g spamd -s /bin/false -d /var/log/spamassassin spamd    
$ sudo chown spamd:spamd /var/log/spamassassin    

Enable autostart and start the service

$ sudo systemctl enable spamassassin    
$ sudo systemctl start spamassassin    

Update spam rules.

`$ sudo sa-update

Configuration steps to use SpamAssassin with Postfix

Edit the master.cf file.

$ sudo vi /etc/postfix/master.cf

smtp inet n - n - - - smtpd

Change the line above to the one below

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

Add the following line to the last line.

spamassassassin unix - n n - - pipe flags=R user=spamd argv=/usr/bin/spamc -e /usr/sbin/sendmail -oi -f ${sender} ${recipient}

Restart Postfix

$ sudo systemctl restart postfix.

Test spam detection

Test by sending the following mail from outside this mail server.

Title: Anything

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

If configured correctly, you will receive an email in your Inbox with a title beginning with [SPAM].

In addition, check the log.

$ journalctl | grep spam.

Automate spam definition updates

Open crontab.

$ sudo vi /etc/crontab

Set up automatic updates (run daily at midnight)

0 0 * * * root /bin/sa-update && /sbin/service spamassassin restart

How to check cron execution

grep "sa-update" /var/log/cron

That's all.