SpamAssassin: Overview

SpamAssassin is a Bayesian spam filter. Bayesian spam filters calculate the probability of a message being spam based upon its contents. Unlike simple content-based filters, Bayesian spam filtering learns from spam and from good mail (ham), resulting in a very robust, adaptive and efficient anti-spam approach. Our system is in its early stages of implementation and will only get better over time.

SpamAssassin uses predefined and custom rules as well as a Bayes database to score messages within a numerical range. The system scores email based upon various characteristics. The characteristics a Bayesian spam filter can look at include:

  • the words in the body of the message, of course, and
  • its headers (senders and message paths, for example!), but also
  • other aspects such as HTML code (like colors), or even
  • word pairs, phrases and
  • meta information (where a particular phrase appears, for example).

How well the anti-spam filter works depends upon recognizing what is considered spam or not considered spam (ham). The SpamAssassin filter can learn what is spam and what is not spam from messages that users specifically mark as spam or not spam by sending them to their junk folder in the web client or via Outlook for ZCO and IMAP. IMAP works with other mail clients as well (i.e. Thunderbird, Apple Mail, etc.). A copy of these marked messages is sent to the appropriate spam training mailbox. Note: Only works with the Junk Folder and not the Junk E-mail folder. 

If you find a message within your Inbox that you determine to be spam, you can highlight it and move the message to your Junk folder. This action helps train the filter to identify and capture similar messages going forward.   

Sometimes a message can be marked as spam and placed within the Junk folder that is not really spam. You should check your Junk folder periodically to ensure that you are not missing any messages. If you or a user find a valid message within the Junk folder, simply move the email to your Inbox. This action will help to train the filter to know that the message is ham (good mail) rather than spam. 

Our previous Spam detection and prevention solution took the approach of blocking spam at a global level, while SpamAssassin will be trained specifically by the users as they mark messages as Junk or Not Junk based upon their individual views of spam. Users also now have the ability to blacklist and whitelist domains or addresses via the web mail client (click here for additional details on this).


With SpamAssassin, users will now receive a daily quarantine digest for their account. The digest will provide you the user with a list of emails that were quarantined or blocked the previous day. To have quarantined emails released, simply click the message ID.  


Related Documentation:

SpamAssassin FAQ

Webmail: Managing Junk Mail

Zimbra Connector for Outlook (ZCO): Junk Folder Management

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