Sign-in & Login Problems

Fix Office 365 SSO Opening Internet Explorer Instead of Edge

Steve K Oct 16, 2026 870 views

Question details

Users need to resolve a sign-in issue where Office 365 Single Sign-On (SSO) authentication incorrectly launches Internet Explorer, causing authentication to fail.

How to Fix Office 365 SSO Opening Internet Explorer Instead of Edge

Product: Office 365
Device & OS: Windows Server 2019
Scenario: Attempting to sign in to an Office 365 work account in a hybrid or Exchange environment after Internet Explorer has been removed or IE mode has been disabled in Edge.
Observed behavior: The SSO authentication process forces Internet Explorer to open instead of Microsoft Edge, frequently resulting in blocked pages or generic error 1200.

Before you start

Verify your server's current Internet Explorer Enhanced Security Configuration (IE ESC) settings and ensure you have administrative privileges to modify the Trusted Sites zone.

Solution 1Recommended

Add Required Security URLs to Trusted Sites

Adding the report server and Microsoft security URLs to your Trusted Sites bypasses IE Enhanced Security Configuration blocks that interrupt the SSO flow.

Even when Microsoft Edge is the default browser, legacy authentication components on Windows Server 2019 may invoke the Internet Explorer engine. If IE Enhanced Security Configuration (ESC) is active, it blocks these silent redirects, breaking the SSO chain.

Open Internet Properties

Press Windows Key + R, type 'inetcpl.cpl' in the Run dialog, and press Enter to launch the Internet Properties window.

Navigate to Trusted Sites

Switch to the 'Security' tab at the top of the window and click on the 'Trusted Sites' checkmark icon.

Add Microsoft Security URLs

Click the 'Sites' button. In the 'Add this website to the zone' field, type your specific report server website and the Microsoft authentication URLs (e.g., https://autologon.microsoftazuread-sso.com) and click 'Add'.

Save Configuration

Click 'Close' on the Trusted Sites window, then click 'Apply' and 'OK' to save your new security configuration. Try the Office 365 sign-in process again.

Add Required Security URLs to Trusted Sites

Server Verification: You may need to uncheck 'Require server verification (https:) for all sites in this zone' if your internal report server does not use an SSL certificate.

Solution 2

Contact Support for Persistent Error 1200

If adjusting Trusted Sites resolves the initial block but results in Error 1200, the issue likely resides in the hybrid Exchange environment configuration.

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Frequently Asked Questions

Why does Office 365 SSO open Internet Explorer instead of Edge on Windows Server 2019?

Windows Server 2019 retains deep system-level integrations with Internet Explorer. Certain legacy authentication prompts and hybrid Exchange setups still invoke the underlying WebBrowser control, which forces IE to handle the request regardless of your default browser settings.

What does Error 1200 mean during an Office 365 sign-in attempt?

Error 1200 is a generic Microsoft Entra ID (formerly Azure AD) authentication error. It usually indicates that the local device state, cached credentials, or Trusted Sites configuration prevented the SSO token from being successfully validated during the login process.

How do I check if Internet Explorer Enhanced Security Configuration is enabled?

You can check this by opening the Server Manager on Windows Server 2019. Navigate to 'Local Server' on the left pane, locate the 'IE Enhanced Security Configuration' property on the right, and see if it is marked as 'On' or 'Off'.

Login & Account Issues