This discussion looks at Sieve scripts — a tool used in Plesk servers outfitted with Dovecot and Warden Anti-Spam — which can lead to rules that filter emails that you should check if something unexplained is occurring it may be that the sieve scripts could be to blame.

The Role of Sieve Scripts in Email Management

Sieve scripts offer a robust mechanism for filtering emails on the server side. They empower users to automate actions such as sorting emails into designated folders, setting up auto-replies, and filtering out spam. Implemented on the server, these scripts process emails before they even hit your email client, serving as a critical defense line against unwanted communications.

A Case Study: The Journey to INBOX.Spam

A recent examination revealed an interesting case where an email, marked as clean by the content filter Amavis, was nonetheless directed to the INBOX.Spam folder. The culprit? A specific fileinto action within a Sieve script, instructing Dovecot to categorise the email as spam. This instance highlights the significant impact Sieve scripts can have on email routing.

How to Access and Modify Sieve Scripts in Plesk

Plesk server users can manipulate Sieve scripts through the web interface or by shell access for those requiring a deeper level of customization. Within the Plesk interface, the “Mail” section offers a gateway to adjusting spam filter settings and managing rules at the individual email account level. For more advanced modifications, including direct Sieve script edits, shell access will be necessary. This approach demands a good grasp of Linux commands and familiarity with Dovecot’s structure.

Sieve Script File Paths and Patterns

Sieve scripts are typically located in the user’s mail directory, with paths varying based on the server’s configuration. Common locations include:

  • /var/qmail/mailnames/
  • /var/qmail/mailnames/

When editing Sieve scripts, you might encounter patterns like:

if address :all :comparator "i;ascii-casemap" :is ["From", "Sender", "Resent-From"] [""] {
fileinto "INBOX.Spam";

This rule directs emails from straight to spam, showcasing how specific patterns in Sieve scripts govern email sorting.

Adjusting Filtering Rules: A Closer Look

The Sieve script shared earlier delineates various rules for email handling, from whitelisting certain addresses to blacklisting others, and employing spam filters based on the X-Spam-Level header. For instance, it includes conditions to file emails from specific senders into INBOX.Spam, underlining the necessity of precise rule configuration to avoid ensnaring legitimate emails.

Best Practices for Sieve Script Management

  1. Review Rules Periodically: To keep your email filtering effective, periodically review your Sieve script rules, especially after changes in email communication patterns.
  2. Proceed With Caution: Exercise caution when modifying Sieve scripts, ensuring your changes are well-tested to prevent unintended email routing.
  3. Back Up Before Modifying: Always back up your existing scripts before making adjustments, enabling easy restoration if needed.


Efficient email management hinges on a fine-tuned approach to spam filtering. By mastering Sieve scripts on your Plesk server, you can enhance your control over which emails land in your inbox versus spam. Regular reviews and cautious customisation of these scripts will ensure your email system remains effective and secure, tailored to your specific needs.