Create a newsletter module enabling the following:
1. User can input their email address to sign up to the newsletter
2. User can also input email addresses of friends to invite to the view the website
3. Emails are saved in a MySQL database
4. Admin can add/delete emails from the database
5. Admin can send a newsletter to all emails in the database.
This does NOT involve integrating with a current CMS. Admin panel you create only requires the functions listed above.
Using a script you have already made is preferable.