Thunderbird has built-in Junk Controls which analyze incoming mail and attempt to identify unwanted messages. Any material classified as Junk can be moved automatically to a designated folder. By default, this is the account's Junk folder. You can change this under:

Tools|Account Settings|<select account>|Junk Settings

Wherever your Junk is put, keep an eye on it and if you see anything has been classified as Junk incorrectly, mark it as Not Junk. You can right-click the message, select Mark, then As Not Junk. Whilst this may not immediately have the effect of ensuring that messages from this sender are never marked as Junk, it is helping the Junk controls learn what is and what isn't junk.

When you see the word Spam, it is very likely that this has come from somewhere outside of Thunderbird. It is quite probable that your Email Service Provider (ESP) is running a spam detection system. There are several things that a spam detector might do to help you manage spam:

  • It might move the message into a Spam folder

  • It might insert a warning into the message's subject line

  • It might insert flags into a message's headers

So, if you have a folder named Spam, and you didn't create it yourself, then chances are that your email program connects to the server using IMAP, and Thunderbird is simply showing you a folder that's been created for you by your ESP's anti-spam system. All you need do is review the contents of this folder from time to time and rescue any material incorrectly put there.

The second and third items in the list above aren't quite as easy to deal with. Message Filters could be set up to identify either of these - a simple test for the word "Spam", possibly with any particular formatting or punctuation, such as square brackets, can be used in a Filter to detect the word inserted into the subject. Similarly a test of the messages' headers for a distinctive word, or even the presence of a custom header could be implemented in a Filter. Thunderbird's Junk Controls offer several ready-made settings to act on headers inserted by some popular anti-spam systems, and if yours is not one of these, it is possible to create a custom filters term to identify headers inserted by another anti-spam system. If you set up such a Filter, then you can have your Spam moved or tagged to make it easier for you to deal with.

The FiltaQuilla add-on provides some enhancements to Thunderbird's Message Filters. One of these is a pair of buttons you can add to your toolbar, which simplify the business of marking messages as Junk and Not Junk.

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