I believe that e-mails are very powerful way to attract visitors to the site and to keep visitors informed about the site content.

Mass email is a good way to inform users about site updates, or downtime or similar announcements. Users consent can be obtained in the "Member Agreement" while registration to send such updates.

Problem
Drupal base version does not have a mass email feature. Emails can be sent via backend but not from drupal GUI.

Solution
There are three possible ways:

1. Advanced user Module can be used to send Mass email. this works in 4.7 from Admin panel.

2. If you want to send mass email based on certain event then you will have to create an Action and use Action module to associate the event with the action. For details see this node.

3. Announcement module is in development stages and is eagerly awaited to help drupaliers implement this feature.