The control for subscribing to the forum feed is not being displayed in my template:
<sf:NotificationSubscription id="notificationSubscriber" runat="server" CssClass="sfforumEmailSubscriberWrp pull-right" />
Users are also not being notified of new posts. I've attached my forum notifications settings dialog for your review.
Then go to Administration » Settings » Advanced » Forums » Notifications and add in SenderProfile the notification profile name you've created/setup in step 2 (by default this is the Default profile). Then select Enable checkbox to enable forums' notifications (see the attached file).
Hope this helps.