Here's the JSON needed to activate the Subscription Tracking app

SMTPAPI.json

{
  "filters":
  {
    "subscriptiontrack":
    {
      "settings":
      {
        "enable":1,
        "text/html":"If you would like to unsubscribe and stop receiving these emails <% click here %>",
        "text/plain":"If you would like to unsubscribe and stop receiving these emails click here: <% %>."
      }
    }
  }
}