Customize the New Post and Thread Activity notifications by going to Settings > Forum > Forum Module Settings. 

New Post Admin Notification


With the Post Approval feature enabled, this email notification is sent to Admins after a new post is posted to the Forum and you determine the Admin Users that are notified by going to Settings > Portal Customization > Navigation & Custom Pages > click the Actions button next to Forum > Edit.


Thread Activity Notification

This email notification is sent to all subscribers of a Thread.