Using adaptive junk filters in Thunderbird
There are a number of strands to our anti-spam efforts, and one is to use the “intelligent” junk mail
controls in Thunderbird. For the purposes of this article we’ll assume that you are already filtering
out messages that are flagged as spam by SpamAssassin – these messages have the {Spam?} flag in
the Subject line. The problem that remains is to deal with the remaining spam messages which have
got through the SpamAssassin checks. This is where Thunderbird’s adaptive (that is to say trainable)
junk mail filter can help.
First you need to train the adaptive filter to recognise the sort of spam you receive. Then, once it has
got the idea, you can tell Thunderbird how to deal with messages that it recognises as spam.
Training the adaptive filter
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Ensure that adaptive filtering is enabled: Choose Junk Mail Controls from the Tools menu and
click the Adaptive Filter tab, and ensure that there is a tick in the box labelled Enable adaptive
junk mail detection, and click OK
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Highlight an example of spam in your INBOX and click the Junk icon in the Thunderbird toolbar. The first time you do this you will see the following message box:
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Click OK to dismiss the message box
The message will be flagged with the Junk icon, like the second item in the list below:
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Highlight another piece of spam and click the Junk icon, and repeat this once or twice
Before long you will find that Thunderbird is marking messages as junk of its own accord.
Sometimes it will be wrong, but often it will be right
When you highlight a message marked as junk you will see an extra warning box telling you that
Thunderbird thinks the message is junk and offering you a button with which to correct it if
necessary:
At first Thunderbird will tend to mark messages from mailing lists and other circulars as junk.
When Thunderbird has marked a genuine message as junk, highlight it and click the This is not
Junk button
When you are satisfied that Thunderbird is not marking too many genuine messages as junk you
can go on to use the Junk Mail Controls
Disposing of junk mail recognised by the adaptive filters
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Choose Junk Mail Controls from the Tools menu
The suggested settings are as follows:
o Do not mark messages as junk if sender is in …: You should probably turn this on, but it
depends how extensive your personal address book is. If it contains a large number of
local users, you may find that the forged headers of spam messages make it appear that
the sender is in your local address book.
o Trust junk mail headers set by SpamAssassin: If you have already dealt with spam that
has been flagged by SpamAssassin, there is no need to tyurn this option on.
o Move incoming messages determined to be junk mail to the “Junk” folder in your
account: this is the usual option to choose. Use this as a holding folder where messages
identified as junk are kept separate to be reviewed, just in case some genuine messages are
mistakenly caught
o Automatically delete junk messages older than 14 days from this folder: You don’t want
your Junk folder to grow indefinitely, but with any automatic deletion option you must be
careful. Check your Junk folder regularly for genuine messages. Particular care must be
taken when you come back to your email after a period away
o When I manually mark messages as Junk: if you are positively identifying a message as
junk you can safely delete it altogether, without holding it for review in the Junk folder
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Click OK
Thunderbird will from now on apply its adaptive filters to your incoming mail.
Checking for false positives
Don’t forget to check your Junk folder for the odd genuine message. If you find any that have been
incorrectly identified as spam take action as follows:
 Drag the message back from the Junk folder into your INBOX
 Open your INBOX
 Point at the message you have just moved back and click the RIGHT mouse-button
 From the pop-up menu choose Mark and then from the second menu choose As Not Junk
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