What were these emails? Were these new topic notifications?
If so, at one point you mistakenly, or not, subscribed to a forum. When the forum upgrade occurred, the default settings changed to send email notifications for forum subscriptions. That is why you suddenly may have been receiving emails when you have not in the past.
If you go to this link, you can unsubscribe to any forums you previously subscribed to:
Then click on the Manage Watched Forums category.