If you want to have e-mail notifications stop, there should be a line in the notification to click on to "unsubscribe".
If you want to delete a thread you started, I think you have to do it in the first 30 minutes after it is posted or else have a moderator remove it.
On some boards, (I think this one, too), if you started the thread, deleting your first post will delete all that followed. Thread is gone.