Back in 2014, the folks at Google responsible for Gmail did something unexpected: They introduced a new email app. On the back end, Inbox was the same thing as Gmail, and worked with your existing Gmail address. But as a user experience, as then senior VP Sundar Pichai explained in a blog post , Inbox was “designed to focus on what really matters.” It was conceived with mobile devices in mind and ditched a decade’s worth of Gmail cruft in favor of tools focused on email efficiency, such as the way it displayed attachments right in the inbox view and incorporated a built-in task manager.

Over the subsequent years, Inbox been a proving ground for features—such as “Smart Reply”—which later made their way into Gmail, especially with the latter’s sweeping new upgrade. So much of Inbox has rubbed off on Gmail, in fact, that it shouldn’t come as a complete shock that Google has decided that Inbox has served its purpose. The company is announcing today that it’s decided to discontinue the app, which will fade away by the end of next March.

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I never got addicted to Inbox myself, but am still saddened by its demise. It arrived during an era of refreshing email invention that had been kicked off by a slick, streamlined app called Mailbox; Inbox seemed like a side bet on Google’s part just in case the new contenders seriously threatened Gmail’s turf. Mailbox itself ended up being discontinued by Dropbox, which had acquired it, back in 2015. Gmail, meanwhile, just keeps rolling along. With that in mind, I can see why Google might consider Inbox to be a bit superfluous.

But I’m also sure that Inbox enthusiasts—some of whom used the app precisely because it wasn’t Gmail—will take the news hard, even if Inbox’s influence on the current Gmail has been profound. (In April, my colleague Jesus Diaz bristled at the density of the new Inbox-inspired Gmail interface and advised people to abandon it for Inbox itself.) And I can’t help but wonder: By retiring Inbox, is Google losing a valuable ability to experiment with new email functionality in a way that’s tough to do with a billion-user mainstay? (Gmail will retain a setting that lets you turn on experimental features not otherwise available in the app.)