https://techcrunch.com/2017/10/18/gmail-launches-its-first-public-ios-beta-to-test-support-for-third-party-accounts/

Google wants to make Gmail the place where you check all your email accounts, not just your Google accounts. The company announced this week it’s testing a new version of the Gmail app on iOS that will allow users to add their non-Google accounts, including those from Outlook (including Hotmail or Live), Yahoo, and elsewhere.

The announcement, which was sent out via a tweet from the @gmail Twitter account, invited users to sign up to test a version of the Gmail iOS app with this new feature.