Autopilot for Moodle intends to tackle reminders and drip emails to students based on their enrollment date, completion data or just straight up calendar events. We’re getting some community feedback at the moment but this does look to be our Fall community funding campaign focus (this will be the most ambitious to date so we’ll likely give it a bit longer to stew).
In the meantime, if you’re looking to accomplish part of that with an existing addon consider Local Reminders. This allows you to setup email reminders for your scheduled calendar events. It can send reminders for Site wide events, course-based events or even user events that are on the calendar. Read more here: http://docs.moodle.org/25/en/admin/setting/local_reminders. The mod is a product of the 2012 Google Summer of Code and was coded by Isuru Madushanka Weerarathna.
Download it at https://moodle.org/plugins/view.php?plugin=local_reminders for 2.5.
The Calendar Reminders plugin creates reminders for Moodle calendar events and sends them automatically to relevant users in a timely manner via Moodle messaging interface. This is a local plugin controlled by the site administrator.