Learning About the Adaptive Filter for Junk Mail Control

Thunderbird's adaptive filter requires that it be trained. You must have both a collection (called a corpus) of good email words and one of bad email words:

• If the good corpus is empty, all the messages are classified as spam.

• If the bad corpus is empty, all the messages are classified as nonspam.

These conditions make it clear that the user must train the spam filter before it can be effective.

Part of the filter's configuration are four preferences. (See Chapter 13, "Customizing Thunderbird for Power Users," for information on setting and resetting preferences in Thunderbird.) Here are the four preferences:

• mail.adaptivefilters.junk_threshold This is the threshold percentage that if a message scores greater than this number, it is considered to be spam. The default is 90%, the same value suggested by Graham.

• mail.toolbars.showbutton.junk This preference determines whether the Junk/Not-junk button is displayed on the Thunderbird toolbar. This button lets you easily toggle a message's status from junk to not-junk, or vice versa.

  Tip

  If you are determined to not start from scratch, you can download a starting filter file. However, these files might not reflect spam as it is today. Training your filter is probably the best option because your nonspam emails can vary from other users' emails in their word contents.

  
  

• mailnews.display.sanitizeJunkMail This setting prevents Thunderbird from displaying images or other content that might contain harmful code (such as viruses).

• mailnews.ui.junk.firstuse The first time the junk mail controls are used, this option displays an information box describing the Thunderbird junk mail (spam) features.

The junk threshold, which is defaulted to 90%, and first use should probably not be modified unless you are sure of the consequences.