https://www.theverge.com/2018/7/5/17537576/google-update-inbox-email-app-apple-iphone-x-gmail

After roughly nine months since Apple’s full-screen iPhone X hit the market, Google has at last updated its Inbox email app to support the device. In a 144MB update pushed out on the App Store today, Google says Inbox now supports Apple’s pricier iPhone variant, with little else by way of changes in the update text.

Effectively, this update just removes the black bars on the top and bottom of the screen so it more naturally fits the iPhone X’s display, with its funky 19.5:9 aspect ratio. For months now, users have been complaining about the lack of support, and Google acknowledged it was working on it back in April following the Gmail redesign.