plone.app.discussion/plone/app/discussion/notifications.zcml

<configure
    xmlns="http://namespaces.zope.org/zope"
    xmlns:zcml="http://namespaces.zope.org/zcml"
    i18n_domain="plone.app.discussion">

    <!-- Plone 3 Event Subscribers -->

    <configure zcml:condition="not-installed zope.app.container">

      <subscriber
          for="plone.app.discussion.interfaces.IComment
               zope.lifecycleevent.interfaces.IObjectAddedEvent"
          handler=".comment.notify_user"
          />

      <subscriber
          for="plone.app.discussion.interfaces.IComment
               zope.lifecycleevent.interfaces.IObjectAddedEvent"
          handler=".comment.notify_moderator"
          />

    </configure>


    <!-- Plone 4 Event Subscribers -->

    <configure zcml:condition="installed zope.app.container">

      <subscriber
          for="plone.app.discussion.interfaces.IComment
               zope.app.container.interfaces.IObjectAddedEvent"
          handler=".comment.notify_user"
          />

      <subscriber
          for="plone.app.discussion.interfaces.IComment
               zope.app.container.interfaces.IObjectAddedEvent"
          handler=".comment.notify_moderator"
          />

    </configure>

</configure>