Symptoms:
Microsoft Outlook keep showing login pop-up / dialog box authentication
Diagnosis:
Conflict on Microsoft Office 2016 account management
Countermeasures:
- Close Microsoft Outlook
- Open another Microsoft Office application instead of Microsoft Outlook (E.g. Microsoft Word, Microsoft Excel, etc.)
- Create blank document
- File > Account > Sign Out
- Then re-open Microsoft Outlook 2016
- Login by type you username and password for authentication
References :
1. https://community.spiceworks.com/topic/2208975-outlook-keeps-asking-password-window-just-flashes-office-365-n-windows-10
2. https://www.stephenhackers.co.uk/outlook-credentials-flashing-and-closing-constantly/