Put a link in the main page that users can click on and subscribe to news.

news/subscribe.php

1. check and see if the user is logged in, if not tell them to log in first.
2. if user is already subscribed, say so and offer them to unsubscribe.
3. Give user a blurb about subscribing and allow them to subscribe.

Subscribing puts a flag in the user_preferences table in the db.

When approving a news item for the main page, check the user_preferences table and send the email to subscribers.