Email subscriptions to discussion board forums and threads are not working.
Blackboard are aware of the issue. While we wait on details of a fix, you can use the Posts section of My Blackboard to view discussion board posts (as well as posts to blogs, journals, wiki edits etc).
Posts are listed with a preview of the content. You can click a link to go to the item in your course, or you can reply within My Blackboard by clicking Reply or Quote.