Incoming spam messages are delivered to mailbox in Plesk

Symptoms

The following Plesk Anti-spam tools are used, however, incoming spam messages are still delivered:

• SpamAssassin Spam Filter
• DKIM, SPF, and DMARC Protection
• DNS Blackhole Lists
• Premium Antivirus for Servers
• Server-wide Blacklist
• Greylisting

Cause

The spam filter detection capabilities are not optimized for the spam that is incoming.

Resolution

The following measures can be applied for spam filter optimization:

1. Decrease spam filter sensitivity (decreasing the number increases the strictness of the filter):

   For one mailbox

   Note: it is possible to edit spam filter sensitivity for the particular mailbox if only the Apply individual settings to spam filtering checkbox is enabled at the Plesk > Tools & Settings > Spam Filter page and the SpamAssassin component for Plesk is installed.

   1. Log into Plesk.

   2. Go to Plesk > Domains > example.com > Dashboard > Mail > Mail Accounts > johndoe@example.com > Spam Filter tab > Press on the Show Advanced Settings link.

   3. Adjust the Spam filter sensitivity and press the Apply button to apply changes.

   Server-wide

   1. Log into Plesk.

   2. Go to Plesk > Tools & Settings > Spam Filter page.

      Note: The SpamAssassin component for Plesk must be installed

   3. Adjust the Required score and press Apply.

2. Train SpamAssassin by using the steps in the following article:

   How to train SpamAssassin on Plesk server?

3. Consider using premium anti-spam tools, such as the following:

   • SpamExperts Email Security

   • Plesk Email Security

4. Lock spammer mailboxes by applying the solution from the following article:

   How to block a particular mailbox or a range of mailboxes belonged to a specific domain from sending emails to Plesk server?