The search giant said Wednesday that it would “say goodbye” to Inbox at the end of March 2019. Google did not say why it was shutting down Inbox, which was released in 2014 and pitched as a more nimble and experimental email app than the older Gmail app.

Google Gmail product manager Matthew Izatt wrote in a blog post that Inbox users can consult an online guide to familiarize themselves with Gmail. He also said, “All your conversations are already waiting for you in Gmail,” meaning that Inbox users won’t have to migrate their stored emails to Gmail.

Since its debut, Inbox has served as a testing-ground for features like “smart replies,” which suggests to people brief replies they can send to others when responding to emails containing certain questions, that have since been incorporated into Gmail.

“Inbox by Gmail has been a great place to experiment with new ideas like snoozing emails to later, as well as try the latest AI-powered experiences like Smart Reply, Nudges and high-priority notifications to help you stay productive,” Izatt said.

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Izatt said that Google recently updated its Gmail app with a new design that includes some of Inbox’s features like “Smart Compose,” which suggests sentences and phrases for people to use in their emails so they spend less time writing.

Inbox now joins a number of now-defunct Google apps including its Spaces messaging app and Google Reader.