How to Set Up a Spam Filter

The filter is enabled by default. You can set system-wide preferences that determine what happens to messages marked as junk. These settings will be used by all your email accounts (although some settings can be overridden in the account settings, as shown below). To access the preferences, click Thunderbird | PreferencesTools | OptionsEdit | Preferences, select the Security panel and then select the Junk tab. 

The configuration in the account preferences for each of your email accounts will override similar settings in the preferences described above. Click ToolsEdit | Account Settings... and select Junk Settings in the left pane for the account to see these settings. 

In order for this filter to be effective, you must train it to recognize the messages that you consider to be junk. To train the filter, simply mark messages as junk. 

You can mark messages as junk in the message list by clicking in the "junk" column in the message list: 

You can also mark messages as junk in the message pane by clicking the Junk button on the message header: 

As you mark messages, Thunderbird learns the characteristics of your junk mail and can start automatically classifying messages. 

Tell Thunderbird what is NOT junk

During the early learning stages, it is a good idea to look at the messages that have been classified as junk and un-flag any that have been incorrectly classified by clicking on the Not junk button.