How to mark messages as junk in Thunder Bird

Step 1: 

Hold the Control key down on the key board (Ctrl) then left click the messages you want to mark as junk they should turn a light blue color.

 

Step 2:

Right click on one of the light blue junk messages and hover over the “mark” category and a sub menu will appear, press the option in the submenu “as junk”

 

Step 3:

Delete the messages from inbox. Right click again on one of the light blue selected junk messages again and chose the “delete selected” option.

Step 4:

All the messages should have been marked as junk and deleted, repeat from step one on any additional messages that you would like marked as junk in the inbox.