Outlook Keep prompting Password in Exchange 2019 CU15 environment
Recently, we encountered an issue in our Hybrid Exchange environment where Outlook repeatedly prompted for credentials for users in a child domain (e.g., xx.abc.com). The issue did not occur for users in the root domain (abc.com). The problem was observed only when users connected from outside the corporate network. Outlook worked normally within the office network and over VPN, but external users experienced continuous password prompts. Firewall checks indicated HTTP 401 (Unauthorized) responses. After troubleshooting, a client-side workaround resolved the issue by applying specific settings on the affected machines. However, this fix would require deployment to all impacted users via Active Directory Group Policy. I would like to understand: Why this issue occurs specifically for child-domain users, and Whether there is a server-side or configuration-based workaround to resolve the issue without deploying registry changes on user machines. Solution for each client's machine: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover Create a DWORD (32-bit) Value. Give it the name ExcludeHttpsRootDomain and the value 1. Create a DWORD (32-bit) Value. Give it the name ExcludeExplicitO365EndPoint and the value 1.
