Forum subscription / Activity e-mail


One of my Xenforo forums isn't really active. It's a working related forum and because there are some days when there are no posts at all, people don't come back often(Users are checking the forum not often.) When I asked the users how I can solve this, they said they would like to receive an e-mail when a new thread has been made.
With Linked-in and Yammer you get weekly e-mails, this really helps to attract visitors.
A forum subscription (every new thread = a new e-mail) or an activity "weekly-newsletter" would seriously help my forum to become more active.
Any ideas on how to solve this "problem" with Xenforo ?