Well to send an email you can use the email module: https://appstore.home.mendix.com/link/app/2461/
For mobile it depends on what you want to do, you could send push notifications: https://appstore.home.mendix.com/link/app/3003/ or you could send a text message with Nexmo for example: https://appstore.home.mendix.com/link/app/2168/
In order to send the message when there are 30 days left you could use a scheduled event and check this: https://docs.mendix.com/refguide/scheduled-events#1-introduction