To deal with large amounts of unsolicited email ("spam" or "junk mail"), Thunderbird uses an adaptive filter that learns from your actions which types of messages are legitimate and which are junk.

Overview

Thunderbird's adaptive filter uses a Bayes algorithm plus training data you have collected to determine which messages it will automatically set as junk. But using an algorithm means a message previously marked as junk is not guaranteed to be automatically marked as junk in the future. If you want a guarantee, see Create filters manually.

To guarantee that important messages will NOT be marked as junk, use Whitelisting.

Also, because junk mail constantly changes, it is recommended to regularly train Thunderbird. Without frequent training, Thunderbird may not deliver good results.

Junk filter settings

Global junk settings

Junk filtering is enabled by default. And you can set global junk settings to tune what should happen to messages marked as junk. These settings will be used for all email accounts (although some settings can be overridden in the Per account settings, as shown below).

1. Click ≡ > Settings > Privacy & Security
2. Scroll down to Junk. Adjust the settings as you see fit.

   

Per account settings

The junk settings in the account settings for each of your email accounts will override similar settings in the Global settings described above.

• Click ≡ > Account Settings > Your email address > Junk Settings

  

How to turn off Thunderbird's adaptive filtering

• Untick Enable adaptive junk mail controls for this account

Whitelisting

Under Do not automatically mark mail as junk if the sender is in you can select address books which will be used as a whitelist. Senders whose email address is in a whitelisted address book are exempt and will not be automatically marked as junk by Thunderbird. But you can still manually marking a message containing a whitelisted address as junk.

It is recommended that you enable whitelisting to help ensure that messages from people you most care about will not be marked as junk.

Training the junk filter

In order for Thunderbird's junk filter to be effective, you must train it to recognize messages that you consider to be junk and messages that you consider to be not junk. If you do not do both, then the filter will not be very effective.

Note also, it is important to mark messages as junk before deleting them. Just deleting a message doesn't train the filter.

Tell Thunderbird what is JUNK

There are several ways of marking messages as junk:

• You can click on the little icon in the Junk column of the Message List Pane:

  

• You can also click the Junk button on the Message Header Pane:

  

• Or you can press J on your keyboard to mark one or more selected messages as junk.

Tell Thunderbird what is NOT Junk

Sometimes Thunderbird's junk filter might get it wrong and mark good messages as junk. Therefore, it is just as important to tell the filter which messages are not junk, especially on a new installation of Thunderbird.

There are several ways of marking messages as Not Junk.

• Click on the Not Junk button in the yellow junk notification below the message header in the Message List Pane:

  

• Click on the red junk icon in the Junk column of the Message List Pane to toggle the junk status of a message:

  

• Or press Shift+J on your keyboard to mark one or more messages as Not Junk.

Repeated training

You should regularly train the filter by marking a number of good messages as not junk - messages in your Inbox and messages that have been filtered into other folders. In this case, you can only use the keyboard shortcut Shift+J, because the Not Junk button appears only for messages that have already been marked as junk. Marking several messages per week will be sufficient, and you can select many messages and mark all of them at the same time.

Unfortunately the user interface does not help you see whether a message has already been marked as "not junk".

Other ways of blocking unwanted messages

Thunderbird's adaptive junk filter is not an absolute barrier against messages from a specific address or specific types of messages. You can have stronger mechanisms to stop unwanted messages by using the following methods.

Create filters manually

You can manually:

• Block some senders.
• Create filters to block messages based on subject or other criteria.

Use an external filter service

You can also use an external filter service to help classify email and block junk.

1. Click ≡ > Account Settings > Your Account > Junk Settings
2. Enable the Trust junk mail headers set by option.
3. Choose an external filter service in the drop-down menu.