How to set up anti-spam policy for debian mail server

This article introduces how to deploy a powerful anti-spam system on Debian mail server, mainly using Postgrey graylist mechanism and SpamAssassin spam filter.

1. Use Postgrey to build a gray list

1. Install Postgrey: Use the following command to install the Postgrey package:

    sudo apt-get update && sudo apt-get -y install postgrey

2. Configure Postgrey: Edit /etc/default/postgrey file, modify POSTGREY_OPTS parameter, and set the delay time (units in seconds, such as 60 seconds):

    sudo nano /etc/default/postgrey

   Set POSTGREY_OPTS to:

    <code>POSTGREY_OPTS="-inet=127.0.0.1:10023 -delay=60"</code>

   Save and start the Postgrey service:

    sudo systemctl start postgrey

3. Integrate Postgrey to Postfix: Edit Postfix main configuration file /etc/postfix/main.cf and add the following line to the smtpd_recipient_restrictions parameter:

    <code>smtpd_recipient_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_unauth_destination, check_policy_service inet:127.0.0.1:10023</code>

   Save and reload Postfix configuration:

    sudo postfix reload

2. Use SpamAssassin to filter spam

1. Install SpamAssassin: Use the following command to install SpamAssassin:

    sudo apt-get update && sudo apt-get -y install spamassassin

2. Configure SpamAssassin: Modify /etc/spamassassin/local.cf file as needed. For example, enable HTML mail verification:

    <code>enable_html_validation</code>

3. Integrate SpamAssassin to Postfix: Edit /etc/postfix/main.cf file and add the following line:

    <code>content_filter = spamassassin</code>

   Save and reload Postfix configuration:

    sudo postfix reload

3. Other anti-spam strategies

In addition to the above methods, you can also consider:

• Blacklist/Whitelist: Configure blacklist and whitelist in /etc/postfix/main.cf to block or allow mail for specific IPs or domains respectively.
• Mail content filtering: Use more advanced mail server management tools to set filtering rules based on email subject or content.

Through the above steps, you can establish a multi-level anti-spam defense system on the Debian mail server. Please adjust the parameters according to actual conditions and regularly monitor the mail server log to ensure policy effectiveness.

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