Office 365 Groups will now have unique mailNickname

Mike McLean (OFFICE)

Hi all,


We've completed an enhancement with the Azure Active Directory team which will now enforce mailNickname to be unique across all Office 365 Groups within a tenant. This will help ensure resiliency across the tenant and facilitate smooth sync scenarios to on-premises.


When Office 365 Groups are created, the name provided is used for mailNickname as well as the first portion of SMTP Address. Previously, Office 365 Group creation did not enforce the mailNickname to be unique across Office 365 Groups. If multiple Office 365 Groups contain the same mailNickname, customers can encounter collisions when these groups are sync’d to on-premises via AAD Connect. In Azure Active Directory, an enforcement has been placed on the mailNickname property so that it will be unique across Office 365 Groups.


Previously created Office 365 Groups that have duplicate mailNicknames will not be affected. If a user attempts to modify the mailNickname property through PowerShell or other means, the service will verify whether the new mailNickname being specified is unique. If not, the modification will be rejected. Additionally, a user can create an Office 365 Group that has the same mailNickname as an Office 365 Group that has been soft deleted. If a user attempts to restore the soft deleted group, they will be prompted to change the mailNickname.


Mike McLean

Office 365 Groups

Senior Program Manager

10 Replies

thanks for the heads-up.

Super a lot of people were waiting for this!

Shouldn't Groups make sure that the mail nickname is unique across all types of mail-enabled objects rather than just inside its own set? Having a synchronisation clash with a DL (for instance) could also be a problem...

Exactly. The alias should be unique across all mail-enabled objects in the tenant.  If I have an ADFS replying party passing mailnickname/alias as a claim for example, any dups will cause problems, just to give another example beyone Tony's .

This is a great observation. For this first step, we're mainly focusing on enforcing uniqueness across cloud-managed Office 365 Groups. One approach we've seen customers use is to build a universal Alias Reservation List that guarantees uniqueness across all their services that create mail-enabled properties, including on-premises.

I really don't think you need anything more complicated than to check all mail-enabled objects (rather than just Groups as you do today) to detect duplicate aliases...

Is it possible to create Office 365 groups created via Team Sites, Planner, Yammer, Stream and Teams with a unique display name? If yes, How?


We would like to prevent the creation of Office 365 groups with duplicate display names in the organization.

Microsoft has committed to delivering a naming policy for Office 365 Groups that might help. Hopefully, we will see news of this at Ignite.


For now, if you want to be sure that Office 365 Groups created using Outlook, OWA, the Outlook and Groups mobile app, or the New-UnifiedGroup cmdlet have names that meet a certain standard, you can use the Exchange Online distribution group naming policy. https://technet.microsoft.com/en-us/library/jj218693%28v=exchg.150%29.aspx?f=255&MSPPError=-21472173...


This policy does not apply to groups created by admins or those created by Teams, Stream, or other Groups-enabled applications.

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