Create a mail filter in Thunderbird to move possibly spam messages to your Junk folder:
- Click the menu button which is located in the upper right hand side of Thunderbird.
2. From the drop down menu, select Tools followed by Message Filters
3. Click the New button to bring up the Filter Rules dialog box
4. Provide a name for your filter.
Filter should be set to match against [SPAM?] in the subject line of all messages.
Action should be set to move matched messages to the Junk Email folder for your mailbox.
When done, click OK to return to the Message Filters dialog box.
5. Confirm that the new filter is enabled for your mailbox and close this dialog box to return to Thunderbird