bbPress Email Notifications is a WordPress plugin by mdodd that provides users with various email notifications relating to forum changes, as well as the ability to turn these notifications off.
It overrides the bbPress-provided ‘Subscribe’ function, allowing users to turn all subscribed topic notifications off and on in one location.
BuddyPress users can update their bbPress email preferences at Member > Settings > Notifications. WordPress users can update their preferences at Users > Your Profile.
This plugin deals solely with bbPress plugin forums, and not with BuddyPress group forums.
Filters are available for modification of plugin behavior.
Download: http://wordpress.org/extend/plugins/bbpress-email-notifications/