The Inbox/Messaging feature did not get a real shot at even being a feature because Spotify took away notifications for new messages. Give Inbox/Messaging some development so users can continue to privately share songs.
Hey folks, we've come back to update this idea status as 'Case Closed'. The inbox feature was recently deprecated within the Spotify app, a necessary but difficult decision that we made after a lot of careful consideration. This feature had extremely low engagement with users and it took a lot of manpower to keep it going.
It's still easy to share and chat about music from your Spotify. Check out this FAQ aboutSharing Music. We're also currently working on new and improved ways to share music and will take this as feedback into the process. So look out for improvements on our Spotify News blog.