If you're using directory synchronization, locate and correct the duplicate attributes. To do this, follow these steps:
Search Active Directory Domain Services (AD DS) for the duplicate msRTCSIP-PrimaryUserAddress attributes. To do this, follow these steps:
On a domain controller, open Active Directory Service Interfaces (ADSI) Edit. To do this, click Start, click Run, type adsiedit.msc, and then click OK.
Create a new query in the AD DS domain in which the users reside. To do this, follow these steps:
In ADSI Edit, in the console tree, click Default naming context, point to New on the Action menu, and then click Query.
Type a name for the query, click Browse under Root of Search, and then select the top-level domain.
Type the following text as the query, and then click OK.
Note Replace firstname.lastname@example.org with the value of the duplicate email address.
Any users who have duplicate msRTCSIP-PrimaryUserAddress attributes are listed in the query results.
The results are listed under Default naming context in the ADSI Edit console tree.
Right-click the user, and then click Properties.
Edit the msRTCSIP-PrimaryUserAddress attributes of the users so that the values are unique within the organization.
Note If you currently have Lync Server deployed on-premises, you’ll want to change the user’s SIP address through the Lync Server Control Panel or the Lync Server Management Shell by using the Set-CsUser cmdlet. For more information, go to the following TechNet blog:
This problem occurs if the value of the msRTCSIP-PrimaryUserAddress attribute or the value of the Session Initiation Protocol (SIP) proxy address is the same for two users in Office 365.
Note Even though the error message specifically states that the value in the local Active Directory isn't unique, you may experience this issue even though you aren't using the Microsoft Azure Active Directory Sync Tool. If you don't use Directory Synchronization, contact Office 365 technical support for help with resolving the issue.