[eluser]Chrisbloom7[/eluser]
I can't say for sure how to integrate it into EE or CI directly as I've never done that, but I have set up plenty of auto mailing scripts in PHP. If you want this to occur on a regular schedule then you'll need to make sure that your host will let you setup a cron task (for an Apache web server).
The basic steps will be getting a list of emails from the database. You can do this using PHP's built-in database functions if you can't hook into your EE/CI database class. Then loop through the results and send the email. PHP has a built-in mail() function that works most of the time, but for more flexibility you could look into using the PHPMailer class, available on Sourceforge. Then just schedule the script to run from the command line in the cron job, with something like `/path/to/php -e your_email_script.php`
There are plenty of tutorials on sending email with PHP and setting a PHP script to run under cron, so if you're still stuck you can always check Google.
Good luck!