Mixpanel allows you analyse the conditions where your users churn from your application and then send targeted emails designed to bring them back. This is an amazingly powerful feature that really bridges the gap between analyzing the data and acting on it.
Mixpanel allows you to directly contact users from the people dashboard via push notifications, sms, and email. After viewing the user history, or filtering on events and metrics, you can send an individual user, or a segment direct messages.
While you're learning how it all works and what emails are effective, you can require emails to be manually approved before they are sent. Very useful for being sure you're not accidently spamming your users.