A link to a message board post on the site where it was generated. It might be a message that starts a thread or it might be a message anywhere within a thread.
To see some examples of the content of board.link:
board.link exists and interaction.sample < 5
Filter for a particular value in board.link:
board.link == "www.xyz.com/msgs/a/123456"
Target service: Board
Always exists: Yes