Unsubscribe (Un)Registered Users (Features)
Emails that are sent out from the forum should have an "Unsubscribe" link to stop receiving emails in response to posts made by the recipient if s/he has put a tick-mark at "E-mail notification on replies in this thread" while submitting the post.
The "Unsubscribe" option should be available for both Registered and Unregistered users.
The Registered users should be able to re-enable it from the control panel after logging in.
The Unregistered users can be presented with a page to (re)start receiving emails from the forum through email verification.
Once an Unregistered user enters an email Id in the relevant box, it should be stored in the database (if it is new) and crosschecked for previous Unsubscribe request.
Moreover, since we have per-post option to receive responses or not, it would be better if the "Unsubscribe" link takes to a page that presents an option to unsubscribe from that particular post or to unsubscribe from all posts.
Similarly, both the above options for re-enabling (re-subscribing).