Using Outlook for Android for personal email and calendar management
If you want the Outlook app, open the Google Play Store, search for "Microsoft Outlook," install it, then sign in with your Outlook account.
If you only want to add the Outlook email to Gmail, open Gmail > profile picture > "Add another account" > "Outlook, Hotmail and Live."
If it still fails, what exact error message do you get?
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Thanks!