Training Thunderbird to recognize junk vs non-junk messages
There are three ways to toggle junk status of selected message(s):

• Open the Tools menu, and choose Mark Selected Messages or Mark Selected Messages as Not Junk.
• Click on the Junk toolbar button.
• Click to toggle the Junk Status column in the message list. (If you do not see it, click the right-most button () in the list header bar and select Junk Status from the pop-up menu.) When you toggle junk status, a trash-can icon will appear or disappear in the Junk status column to indicate the junk status of the selected message.

Enabling Junk Controls

• Open the Tools menu and choose Junk Mail Controls.... Enable the feature for your mail account, and Mozilla will automatically classify incoming messages. (See Junk Mail Controls Options.)
• If you have trained it on virus mail, consider disabling the white listing (many mail viruses send bulk messages to people in the address book of the infected computer).
• Make sure to correct the Junk Mail Controls when it incorrectly labels messages either as junk or not junk.
• To analyze existing messages, select messages, open the Tools menu and choose Run Junk Mail Controls.

Note: Thunderbird will only run Junk Mail Controls when the training database has information on non-Junk messages. If Junk Mail Controls does not work, select some messages and explicitly mark them as Not Junk.

Junk Mail Advanced Settings
To fine-tune how Junk Mail Controls works, open the Tools menu and choose Junk Mail Controls...:

• Account: Choose an mail account to change the Junk Mail Controls settings for that account. (Note: all accounts share the same Junk training database.)
• Junk Mail Log: Click the button to open a dialog showing you the history of Junk mail detections. You can disable Junk Mail Log from the dialog.
• Enable Junk Mail Controls: Toggle this option to activate or deactivate junk mail classification.
• Do not mark messages as junk mail if the sender is in my address book: Choose this option to prevent messages from people you know inadvertently classified as junk mail.
• Move incoming messages determined to be junk mail to: Check this option to automatically move messages flagged as Junk to a special folder.
• • "Junk" folder on [account]: select this to use the default Junk folder.
  • Other: [account]: select this to choose your own custom-named junk folder.
  • Automatically delete junk messages older than __ days from this folder: If you are confident old messages classified as junk are indeed junk mail, check this option to automatically delete old junk messages after a grace period.
• When I manually mark messages as Junk: Choose this to set what you want Thunderbird to do when you manually mark messages as Junk.
• • Move them to the "Junk" folder: Choose this to move manually-marked Junk messages to the Junk folder.
  • Delete them: Choose this to move manually-marked Junk messages to the trash folder.