Tenant Migration

Resolve Duplicate Microsoft Entra ID Accounts in Exchange Hybrid

Kushani Nimanthika Oct 1, 2026 868 views

Question details

The user needs to handle duplicate accounts between on-premises Active Directory and Microsoft Entra ID during the setup of an Exchange Hybrid deployment.

How to Resolve Duplicate Microsoft Entra ID Accounts in Exchange Hybrid

Product: Microsoft Exchange and Entra ID
Device & OS: not provided
Scenario: Planning or executing directory synchronization in an Exchange Hybrid environment where existing Microsoft Entra ID accounts might conflict with on-premises Active Directory accounts.
Observed behavior: Synchronizing without preparation leads to attribute conflicts, account matching failures, and authentication issues because synchronization does not automatically prioritize competing values.

Before you start

Ensure you have a complete backup of your on-premises Active Directory and have mapped out a rollback plan before initiating any directory synchronization tools.

Solution 1Recommended

Assess and Resolve Duplicate Identities Before Synchronization

Identify and fix duplicate source anchors, domains, and conflicting attributes before running Microsoft Entra Connect.

Do not begin synchronization until the directory has been fully assessed. Synchronization does not provide a simple priority setting for retaining every competing value; therefore, attribute flow and source authority must be planned in advance.

Run Directory Assessment Tools

Download and run the Microsoft IdFix DirSync Error Remediation Tool to identify duplicate or invalid attributes (like UPNs or proxyAddresses) in your on-premises Active Directory.

Resolve Conflicting Attributes

Manually update the on-premises AD accounts or the existing Microsoft Entra ID accounts so that UserPrincipalName (UPN) and primary email addresses match correctly without unintentional duplication.

Plan Source Authority

Determine which directory will act as the authoritative source for specific attributes and configure your synchronization rules accordingly.

Assess and Resolve Duplicate Identities Before Synchronization

Attribute Flow Limitation: There is no built-in priority setting to pick and choose individual competing values during a conflict. The designated source of authority will overwrite the target.

Solution 2

Engage Support and the Hybrid Management Community

Consult experts when dealing with complex tenant migration or extensive duplicate identity scenarios.

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Frequently Asked Questions

How are conflicts handled when matching accounts have different values, such as passwords?

During synchronization, the designated source of authority (usually the on-premises Active Directory) will overwrite the target directory. If Password Hash Sync is enabled, the on-premises password hash will replace the existing Microsoft Entra ID password.

Can I define a priority or choose which attribute value is retained during synchronization?

No, synchronization does not provide a simple priority setting for retaining individual competing values. You must plan the attribute flow and establish the source of authority before running the sync to prevent data loss.

What tool should I use to find duplicate accounts before deploying Exchange Hybrid?

Microsoft recommends using the IdFix DirSync Error Remediation Tool. It scans your on-premises Active Directory to discover and help you remediate duplicate or invalid attributes before you begin synchronization with Microsoft Entra ID.