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Training Thunderbird's Junk Filter


About the Thunderbird Junk Filter :

No one likes to have to deal with junk email. With Thunderbird, there are two tiers of protection to separate you from junk email/spam: SpamAssassin on the email server and Thunderbird's integrated junk filter.

The first part to reducing your junk mail in Thunderbird is to set up a SpamAssassin filter. See the document Setting up the SpamAssassin Filter for directions. Once you have the SpamAssassin filter in place, you can start training Thunderbird's junk filter.

Thunderbird comes with an integrated junk filter but it needs to be "trained" to know what is "junk email " and what is "legitimate email". When you first start using the Junk filter, you will need to spend some time telling Thunderbird what is good and what is junk and correcting when it makes mistakes. Once it is trained though, the Junk filter is usually very accurate and will help catch the junk email that even SpamAssassin misses.


How to turn on the Junk Filter :

Thunderbird's integrated filter is turned on by default but will not start labeling email as junk immediately. There is a delay so that Thunderbird can get an idea of what type of email you receive and what you consider junk before it starts. How long this delay is depends on how much junk you receive.

If you wish to make sure the integrated junk mail is turned on,

  1. In Thunderbird, click on Tools
  2. Click on Account Settings from the menu.
  3. Click on the Junk Settings under SCLS-POP
  4. Make sure that Enable adaptive junk mail controls for this account is checked.

Thunderbird Account Settings for Junk

Because Thunderbird will make a number of mistakes when you're training the filter, we recommend you do not check the "Move new junk messages to:" option. This way all Thunderbird identified junk will go to your In box where you can easily find and confirm that it is junk or correct it if it is legitimate email.


How to train the Junk filter that something is Junk :

Thunderbird's junk filter starts off "blank" and learns based on what you tell it is and is not junk. If you followed the directions for setting up the SpamAssassin filter, Thunderbird's junk mail filter will automatically be trained that items caught by SpamAssassin are junk.

When you recieve a junk email that was not caught by SpamAssassin, you can tell Thunderbird the item is junk by:

  1. Right click on the junk email
  2. Select Mark
  3. Click on As Junk

Mark an Email as Junk in Thunderbird


  1. In the Flame icon colum for the email, click on the little circle.
  2. When it changes to a flame, the email is marked as junk.

Mark as Junk Using Flame Column in Thunderbird

Once the email is marked as junk, you can move the email to your Junk folder or you can delete it. You may need to tell Thunderbird something is junk a few times before that type of junk mail gets automatically flagged as junk.


How to train the Junk filter that something is not junk:

Because Thunderbird learns based on what is marked as junk, it's very important that you mark any email incorrectly labeled as junk as "not junk". Otherwise Thunderbird will consider to mark emails like that as junk in the future. This will be especially important when Thunderbird is just starting to learn, but will improve the more you train it.

Just like it was for Eudora, you will want to check to make sure that non-junk email hasn't been marked as junk, especially when Thunderbird first starts marking email as junk.

  1. Right click on the email incorrectly marked as junk
  2. Select Mark
  3. Click on Not Junk

Mark an Email as Not Junk


  1. In the Flame icon colum, click on the flame icon for that email.
  2. When it changes to a little circle, the email is marked as not junk.

Mark as Not Junk using Flame Column