For my lot, they don't. I have 'Forum Post' Pages in the course that directs students to each topics forum. They can then optionally subscribe for email.
I try to avoid emailing all the students as I am on a shared host ISP server while I try all this out (I'm a newbie) and I get blocked from people like qq.com and 163.com (public accounts like hotmail and gmail) if I send more than 50 messages in an hour.
I suppose, if you needed an email to go out, you could try restoring most of the forum posts from the backup and then recreating the first of each forum so that it's then emailed to your students.