Dealing with Junk E-mail Mozilla Thunderbird

Dealing with Junk E-mail
Mozilla Thunderbird supports many different methods for dealing with junk email (also known as "spam"). This document will describe the ways Thunderbird can deal with junk mail so you don't have to waste your time doing so.

Thunderbird's Junk Mail Controls
Junk mail controls can be set separately for each email account or, if using the global inbox feature, to all local folders. These are the available options for determining how Thunderbird should recognize and treat junk mail.

General Options
Do not mark messages as junk mail if the sender is in my address book prevents messages from being automatically marked as junk mail if the sender is listed in the selected address book. This is effectively a White List of contacts whose messages should never be treated as junk mail, and is often most useful when combined with the Automatically add outgoing email addresses to my Address Book option.
Trust junk mail headers set by will automatically recognize mail that is marked by a separate junk mail filtering program. Very often, your ISP or mail server will install such a filtering program, which adds special headers to your email before it is retrieved by Thunderbird. By setting this option, you do not have to create special filters to recognize these. Currently supports: SpamAssassin and SpamPal.
If SpamAssassin is selected, the filter checks the content of the X-Spam-Status and X-Spam-Flag headers, as well as whether **SPAM** has been inserted in the subject line of the message.
If SpamPal is selected, the filter checks the value of the X-SpamPal header.
Thunderbird reads the settings used to look for junk mail headers from files with a .sfd extension that are in the Thunderbird profile directory.

Handling
Determines what to do with junk mail when it is received
Move incoming messages determined to be junk mail to will automatically place junk mail into the specified folder upon arrival
Automatically delete junk messages older than will automatically empty the chosen junk folder and totally delete the messages
When I manually mark messages as Junk allows the user to determine whether to put manually-marked junk mail into the Junk folder or delete it immediately
When displaying HTML messages marked as junk, sanitize the HTML

Logging
Clicking the Junk Mail Log button brings up another option setting window that allows you to enable and disable logging of junk mail filtering, as well as view the log itself. Normally, it should not be necessary to enable logging.

Adaptive Filtering:
Thunderbird's primary method of dealing with junk mail is an adaptive filter. Thunderbird's adaptive filter actually learns how it should classify e-mail by learning from your habits.
If you consistently mark a certain type of e-mail as junk, Thunderbird will learn that that type of e-mail should be marked as spam in the future. However, e-mail that you wish to receive will not be marked as spam, because Thunderbird's filter is entirely based on your actions.
The filter improves as it watches how you sort your e-mail, and with time the filter will reach nearly 100% classification accuracy. More important, however, is that the filter is intentionally conservative in what it marks as junk mail. If Thunderbird can't quite decide whether an e-mail is junk or not, it will mark it as not spam. It's that simple -- after training, the filter simply doesn't create false positives.

Source:http://wiki.mozilla.org/Thunderbird:Help_Documentation:Dealing_with_Junk_E-mail