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How to Configure Entra Cloud Sync in an Exchange Hybrid Environment

Maira Mehtab Sep 27, 2026 868 views

Question details

The user is looking for guidance on introducing Microsoft Entra Cloud Sync into an existing Exchange hybrid environment where there are separate on-premises and cloud accounts.

Product: Microsoft Exchange / Entra ID
Device & OS: not provided
Scenario: Deploying Entra Cloud Sync in a network environment running an Exchange hybrid setup alongside pre-existing, separate on-premises and cloud identities.
Observed behavior: Without proper configuration, integrating these directories causes authentication issues, access problems, and duplicate accounts due to identical usernames not matching correctly.

Before you start

Before making changes to your synchronization settings, comprehensively audit your active directory to identify any duplicate usernames between on-premises and cloud environments to prevent hard-matching conflicts.

Solution 1Recommended

Review Identity and Hybrid Configuration for Entra Cloud Sync

Properly mapping identities and verifying your Exchange hybrid prerequisites is crucial to avoid management and authentication problems when enabling Entra Cloud Sync.

While Entra Cloud Sync can be safely introduced after an Exchange hybrid setup is configured, the presence of separate on-premises and cloud accounts with the same username requires strict identity matching.

Failing to review existing hybrid configurations may result in incorrectly matched accounts, locking users out of their mailboxes or duplicating identities in the directory.

Audit existing accounts

Use PowerShell or your Active Directory administrative center to list all on-premises accounts and cross-reference them with your Entra ID (Azure AD) cloud accounts to identify matching usernames.

Configure identity matching

Ensure that the immutable ID (Source Anchor) or user principal name (UPN) is properly mapped so that the Entra Cloud Sync agent links the on-premises user to the existing cloud identity rather than provisioning a new one.

Deploy in a test Organizational Unit (OU)

Before rolling out sync to the entire organization, scope the Entra Cloud Sync configuration to a specific test OU containing a few pilot accounts to verify that synchronization and mail flow operate smoothly.

Consult official documentation

Refer to the Microsoft Entra Cloud Sync and Exchange hybrid deployment guides, and validate specific attributes required for Exchange hybrid writeback.

Seek Community Assistance: If you encounter specific attribute synchronization errors, consider posting detailed logs to the Microsoft Exchange Hybrid Management community portal for specialized guidance.

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Frequently Asked Questions

Can Entra Cloud Sync and Azure AD Connect coexist in an Exchange Hybrid environment?

Yes, Entra Cloud Sync can be deployed alongside Azure AD Connect, provided they are scoped to target different sets of users or Organizational Units (OUs) to avoid synchronization conflicts.

What happens if I have identical usernames on-premises and in the cloud?

If they are not properly matched using a Source Anchor or UPN before enabling sync, Entra Cloud Sync may create duplicate accounts or cause authentication failures. You must carefully review your identity matching configuration.

Does Entra Cloud Sync support Exchange Hybrid writeback features?

Yes, Microsoft supports Exchange hybrid setups with Entra Cloud Sync, but it requires specific configuration steps to ensure that Exchange-specific attributes are successfully written back to your on-premises Active Directory.

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