Welcome to FlyerTalk! I cannot help you with getting email notifications for forum subscriptions, but in case you're not already aware, the MyFlyerTalk feature may work equally well or better:
If you set MyFlyerTalk as your FT bookmark, you can easily check in to see the status of your subscribed threads and forums. In the screenshot below, subscribed threads with new activity appear at the top (orange box) — only threads with new posts are listed. Subscribed forums with new posts or threads are indicated by a bulletin board icon with two papers (green circle), while forums with no new activity have a greyed out icon with only one sheet of paper (purple circle):