Exchange Connection Problems

How to Fix Hybrid Modern Authentication Error 2002 in Exchange Outlook

Anum Mushtaq Oct 15, 2026 869 views

Question details

Users are unable to complete authentication in Outlook desktop, receiving error code 2002 despite successfully reaching the AD FS page.

Troubleshooting Hybrid Modern Authentication Error 2002 in Exchange

Product: Microsoft Outlook / Exchange
Device & OS: not provided
Scenario: Configuring Hybrid Modern Authentication (HMA) for a mixed on-premises Exchange and Exchange Online environment.
Observed behavior: Outlook desktop successfully displays the AD FS login page but fails to authenticate the session, throwing error 2002 instead of granting access.

Before you start

Ensure you have administrative access to both your on-premises Exchange server and the Microsoft 365 Admin Center. Verify that your Active Directory Federation Services (AD FS) endpoints are publicly accessible and that SSL certificates are valid and correctly bound.

Solution 1Recommended

Review HMA Configuration and Auth Provider Settings

Check your on-premises Exchange server for misconfigured EvoSTS authentication providers or missing OAuth configuration settings.

Error 2002 typically occurs when the on-premises Exchange server fails to properly validate the OAuth token provided by Exchange Online or AD FS. This usually points to a missing or misconfigured Authentication Provider (EvoSTS) setup in the on-premises environment.

To resolve this, you must ensure the EvoSTS authorization server is correctly registered and that the OAuth token configuration parameters align between the cloud and on-premises environments.

Open Exchange Management Shell

Verify Authentication Server Configuration

Run the command `Get-AuthServer` to verify that the EvoSTS authentication server is present, enabled, and correctly configured for your hybrid setup.

Test OAuth Connectivity

Run `Test-OAuthConnectivity -Service EWS -TargetUri <Your_EWS_URL> -Mailbox <Test_Mailbox>` to pinpoint where the authentication handshake is failing.

Update AD FS Relying Party Trust

Open your AD FS Management console and verify that the correct claim rules are in place for Microsoft 365, ensuring tokens are properly passed to your on-premises environment.

Restart IIS Services

Run `iisreset` in the command prompt to clear the cache and enforce the updated authentication policies across all Exchange services.

Review HMA Configuration and Auth Provider Settings

Dedicated Support Forums: Because hybrid setups involve complex routing, consider posting detailed logs in the Microsoft Exchange Hybrid Management support area if the issue persists.

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Frequently Asked Questions

What is Hybrid Modern Authentication (HMA)?

Hybrid Modern Authentication is an identity management framework that allows on-premises Exchange servers to utilize the same advanced OAuth-based authentication methods, such as Multi-Factor Authentication (MFA) and Conditional Access, as Exchange Online.

Why does Outlook reach the AD FS page but still fail with Error 2002?

Reaching the AD FS login page means the client successfully found the federation endpoint. Error 2002 occurs subsequently because the on-premises Exchange server cannot validate the returned OAuth token, usually due to missing AuthServer configurations, mismatched TLS certificates, or outdated EvoSTS attributes.

How do I verify if HMA is currently enabled in my Exchange environment?

You can check the HMA status by running the `Get-OrganizationConfig | Format-Table Name,OAuth*` cmdlet in the Exchange Management Shell. If the `OAuth2ClientProfileEnabled` parameter is set to True, Hybrid Modern Authentication is actively enabled.

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