Are inactive users sent notifications?

Users are typically active during a Challenge. But to help establish activity, there are automatic notifications that go to users when they're inactive. There are a variety of messages relayed, but they provide tips, encourage the user to try a specific Action, or just generally encourage activity.

These notifications are generated after each of the following periods of inactivity:

36 hours of inactivity (new user) 

4 days of inactivity

15 days of inactivity

30 days of inactivity