Tackle spam with SpamAssassin on CentOS 7 & Postfix

Table of contents

Intro

On some cases you need to maintain your own mail server, for example for development purposes. This article is another quick technical walkthrough, on how to install SpamAssassin to accompany Postfix on CentOS 7 Linux platform.

Prerequisites

The following assumptions are made:

• CentOS 7.2
• Postfix 3.1 (same configuration works on 2.10 also)
• SpamAssassin 3.4.0

You can check the Postfix version with

postconf -d | grep mail_versionCopy

And the SpamAssassin version with

spamassassin -VCopy

Install and configure SpamAssassin

Install SpamAssassin

yum update
yum install spamassassinCopy

Configure SpamAssassin by editing the configuration file

vi /etc/mail/spamassassin/local.cfCopy

Uncomment, or insert the following:

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

Add new user to run SpamAssassin. ** -g = add to group spamd, -s /bin/false = No shell (does not mean, cannot access via SSH!), -d = home dir **

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

Enable (if not automatically enabled) and start the service

systemctl enable spamassassin
systemctl start spamassassinCopy

Update the spam rules by running

sa-updateCopy

Configure Postfix to use SpamAssassin

Configure the Postfix by editing the master.cf configuration file.

Open conf in editor

vi /etc/postfix/master.cfCopy

On the top, replace

smtp      inet  n       -       n       -       -       smtpdCopy

with

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

Add this as the last line:

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

Restart Postfix

systemctl restart postfixCopy

Test the spam detection

Test, by sending an email outside of this mail server.

Title does not matter, enter XJS*C4JDBQADN1.NSBN3*2IDNEN*GTUBE-STANDARD-ANTI-UBE-TEST-EMAIL*C.34Xas the message body.

If all went well, your inbox should now have an email with a title beginning with [SPAM].

You shoud check the logs, what just happened, by querying journal with:

journalctl | grep spamCopy

Automate the spam definition updates

Automatic definition updates with cron (run every night at 01.00)

00 01 * * * root /bin/sa-update && /sbin/service spamassassin restartCopy

Check, that it has been run:

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

There we go, most spam should now be marked as such.

Further reading

SpamAssassin docs.