How to Reinstall Azure AD Connect After Active Directory Changes
Question details
The user needs to reinstall or reconfigure Azure AD Connect after rebuilding an on-premises Active Directory and wants to know the best method to synchronize users without causing network disruptions or password resets.
- Product
- Azure AD Connect
- Device & OS
- not provided
- Scenario
- Synchronizing a rebuilt on-premises Active Directory with Microsoft 365 Azure AD.
- Observed behavior
- To ensure user identities, sign-in names, and access are preserved during directory synchronization using the correct UPN and source anchors.
Before re-enabling synchronization, ensure that all on-premises user accounts are fully rebuilt and verified, and identify the correct User Principal Name (UPN) format matching your Microsoft 365 environment.
Match and Synchronize Users Using UPN and Source Anchor
Use this method to safely link rebuilt on-premises AD users to existing Azure AD accounts using consistent UPNs rather than relying solely on email addresses.
When you rebuild an on-premises Active Directory, user object GUIDs change. To prevent creating duplicate accounts in Microsoft 365 or deleting existing ones, you must carefully match on-premises users to existing cloud accounts using the correct User Principal Name (UPN) and source anchor.
Synchronizing based on an email address format that matches the Azure AD UPN (e.g., user@company.com) is generally preferable to renaming all local logon names.
Ensure all users in your on-premises Active Directory are recreated using the identical naming convention (e.g., user@company.com) as your existing Azure AD accounts.
Create a dedicated test OU in your on-premises Active Directory and place a single test user account inside it.
Launch Azure AD Connect, navigate to the filtering options, and scope the directory synchronization to only include the newly created test OU.
Execute a delta or initial sync in Azure AD Connect to verify that the test account links correctly to the cloud identity without duplicating or deleting data.
Once the test user synchronizes successfully and the UPN matches, re-run the Azure AD Connect wizard to deploy synchronization for the entire organization.
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Frequently Asked Questions
Will reinstalling Azure AD Connect automatically change user passwords?
No, reinstalling or reconfiguring Azure AD Connect does not automatically change user passwords. Passwords will only be updated or overwritten if Password Hash Synchronization (PHS) or another specific password policy is actively configured and synced.
Will users be disconnected from the network during Azure AD Connect reconfiguration?
Reinstalling the sync engine itself does not disconnect users from your local network. However, once identities successfully sync to the cloud, users may be required to sign in again to their Microsoft 365 online services.
Should I change all on-premises user logon names before syncing?
It is usually not necessary to disrupt the network by changing all local logon names (like firstinitial.lastname) if your UPNs or email address fields correctly match the Azure AD identities. Synchronizing with the correct UPN format (e.g., user@domain.com) is generally the preferred and safer method.
How can I safely test Azure AD synchronization after rebuilding the directory?
Move a single user into a dedicated test Organizational Unit (OU) in your on-premises AD. Configure Azure AD Connect filtering to sync only that specific OU. This allows you to verify that the identity matches correctly in the cloud before deploying the sync settings to the entire organization.
