How to Unsubscribe Some Guest Users Manually who have earlier Subscribed to a Discussion

Background
In Easydiscuss, as its a functionality where in
> Guest user (who has not registered) can add a reply
> also when a setting enabled in back end they are automatically subscribed to a post

So - when a new reply is added - these guest users also receive a reply notification

Issue
When we checked our easydiscuss - we found that some of the user email address is incorrect due to which mail is bounced when a notificaton on new reply is added

Need Solution for
How i as a admin can unsubcribe those users from getting new notfication
We have close to 1500 posts with different email and around 50 email address which are incorrect
How i as admin can unsubscribe these 50 users from getting new notification email replies

Thanks