SpamAssassin Spam Filter

SpamAssassin & Spam Filter Management

To achieve the desired level of spam protection, Plesk lets you configure a number of SpamAssassin settings, namely:


  • Spam Filter Sensitivity

    To identify spam messages, SpamAssassin performs a number of different tests on contents and subject line of each message. As a result, each message scores a number of points. The higher the number, the more likely a message is spam.

    For example, a message containing the text string “BUY VIAGRA AT LOW PRICE!!!” in the Subject line and the message body scores 8.3 points. By default, the filter sensitivity is set so that all messages that score 7 or more points are classified as spam.

    If your users still receive spam messages with the default sensitivity, increase it by setting a lesser value, for example, 6. If SpamAssassin marks valid messages as spam, decrease the sensitivity by setting a higher value.

  • Spam Marks

    At the server level, you cannot set the server-wide spam filter to automatically delete spam: you can do it only on a per-mailbox basis. So, for the server-wide policy, you can choose only marking messages as spam: X-Spam-Flag: YES and X-Spam-Status: Yes headers are added to the message source by default. If you want, the spam filter will additionally include a specific text string to the beginning of the messages’ subject line (by default, this string is *****SPAM*****). Though you cannot configure SpamAssassin to delete all spam messages, you can let each mailbox owner configure their own spam protection settings. This includes, for example, setting their spam filters to automatically delete messages marked by SpamAssassin, or setting up their personal black and white lists. 

  • Maximum size of messages to check

    Analyzing a huge number of emails can heavily increase the load on your server. To avoid this, you can set the maximum size of the message that the spam filter will test.

  • Number of SpamAssassin processes

    Another way to limit the server loading by SpamAssassin is defining the maximum number of SpamAssassin processes (on Linux) or threads (on Windows) running simultaneously on the server. In Plesk for Linux, the maximum number of SpamAssassin processes you can configure via the Plesk GUI is 32. If you require more SpamAssassin processes to run simultaneously, add the following lines to the panel.ini file:

    spamAssassin.maxChildrenLimit = 80

    where the numeric value indicates the maximum number of SpamAssassin processes that can be configured in the Plesk GUI.

    • (Plesk for Windows) Trusted languages and locales

      You can define the language characteristics of mail that should always pass the filter by specifying trusted languages and locales. Letters written in the specified languages and with the defined character sets will not be marked as spam.

    • Black and white lists

      SpamAssassin lets you include certain senders into its black and white lists:

      • If you want the emails from specific domains or individual senders to be always treated as spam, add the respective entries to the spam filter’s black list. SpamAssassin will add the USER_IN_BLACKLIST mark to the header of each email from the specified addresses to guarantee that this email will be processed as spam. As a result, the email will be marked as spam, deleted, or placed to the Spam folder, depending on the SpamAssassin settings specified for the whole server and for a particular mailbox.
      • If you want to be sure that you and your users will not miss email from specific senders, add email addresses or entire domains to the spam filter’s white list.