Additional to Mike
Use a scheduled event to check nightly if reminders needs to be send and if, send them
For sending emails, you can use the Email Templates module from the Marketplace ( https://marketplace.mendix.com/link/component/259 ). This module has examples of how to send an email with information like the from and to address, subject line and body populated with information from your app. After you’ve installed this module and have it running, you should post any further questions in the Forum.
Hope that helps,