The notify module gives you a simple way to let members track pages that are important to them, and receive updates by email when there are changes.
1) Watch any page, section of your site, or your entire site.
2) Be notified instantly or through a daily or weekly digest.
3) Easy markup -- just put [(notify)] on a page, header, or action bar.
4) Allow members to customize their own notify settings.
5) Runs automatically (using cron).