Intended Audience: People experiencing Authentication Failure with Outlook 2016 for macOS and O365.
- Outlook 2016 for macOS stopped being able to connect to O365 and check mail, no error displayed at this stage.
- Credentials are definitely correct, still able to access O365 mail via iOS app and browser.
- Deleting and re-adding the account within Outlook now throws up “Authentication Failure”.
- Uninstalling and re-downloading Office 2016 for macOS made no difference.
Thank You Larry: Original solution article
Seems that the issue is caused by corruption of KeyChain entries related to Outlook.
- Go to KeyChain Access
- Search “Exchange” under Login –> All Items and delete everything
- Search “Office” and delete everything
- Search “ADAL” and delete everything
- Launch Outlook, try again