Sync errors detected on your Azure AD Connect servic

Biztechline Consulting 1 Reputation point

Hi Guys,
I run an infrastructure with a single DC and had all users account synced with office 35 (azure ad connect) previously all was working fine till the DC died and couldn't restore from the back. So, I created a new DC and resynced all account again with Ms Office 365 (Azure AD connect) so far, the accounts where synced but we previously had synced with the old DC and not we are getting: Sync errors detected on your Azure AD Connect service.

All accounts have synced but with extensions at the end, for example,
The idea is to keep all defaults
Any idea how to achieve that? Remember we had previously synced and that DC no longer exist! We have a new DC and sync all the accounts again.

Azure Active Directory
Azure Active Directory
An Azure enterprise identity service that provides single sign-on and multi-factor authentication.
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  1. Marilee Turscak-MSFT 22,301 Reputation points Microsoft Employee

    Hi @Biztechline Consulting ,

    I understand that you were unable to restore your old domain controller, but created all of your accounts in a new domain controller and synchronized them to your tenant.

    After synchronizing the accounts, the UPNs all have numbers added to firstname.lastname such as

    This issue occurs because the users exist in both your on-premises directory and in Azure and you have duplicate UPNs.


    1. ) Delete the duplicated accounts from Microsoft 365 and make sure that they are removed from the "deleted users" section of the portal. Remove-MsolUser -UserPrincipalName <duplicateaccounts@keyman .com> -RemoveFromRecycleBin

    2.) Hard match or soft match the users so that Azure AD Connect knows that they refer to the same user.

    There is a very good explanation of hard matching and soft matching here:

    The hard match is attempted before the soft match is attempted. If there’s no match, a new user object is created in Azure AD to correspond to the user object in the on-premises Active Directory environment.

    Additional resources:
    Number added to user names and email addresses when users are synced to Azure AD
    Azure AD Connect: When you have an existing tenant
    Azure AD Connect - Dealing with incorrectly created users post-sync
    Restore deleted Microsoft 365 Hybrid User

    Let me know if this helps and don't hesitate to ask if you have further questions.


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