Inbox by Gmail was an experimental email app, offering users features like snoozing emails to check later, Smart Reply, high-priority notifications, and more. The company says that in the four years of the app's life it has "learned a lot about how to make email better," adding some of the most popular Inbox features directly into its main Gmail client.
Because of this, and to maintain a "more focused approach," Google will shutter Inbox by Gmail and focus entirely on Gmail.
Four years after launching Inbox in 2014, we've learned a lot about how to make email better—and we’ve taken popular Inbox experiences and added them into Gmail to help more than a billion people get more done with their emails everyday. As we look to the future, we want to take a more focused approach that will help us bring the best email experience to everyone. As a result, we’re planning to focus solely on Gmail and say goodbye to Inbox by Gmail at the end of March 2019.In an effort to help users transition from Inbox to Gmail, the company has set up a new guide on its support website. Google says that the new Gmail, which launched in April, will be a nice home for former Inbox users since it incorporates many of the same features as Inbox, as well as some new ones.