When you use the Microsoft Azure Active Directory Sync Tool to sync your on-premises Active Directory Domain Services (AD DS) environment to Microsoft Office 365, you notice that mail-enabled groups that have an email address aren't synced to Office 365.
This issue occurs if a display name isn't specified for the on-premises mail-enabled group.
Important This section contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more info about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 How to back up and restore the registry in Windows
To fix this issue, make sure that the on-premises mail-enabled group has a display name. You can use a tool such as Active Directory Service Interfaces Editor (ADSI Edit) or the LDP tool to populate the displayName attribute for the mail-enabled group in the on-premises AD DS environment.
The following procedure describes how to edit a display name by using ADSI Edit.
On a domain controller or a computer on which the Windows Server Administration Toolkit is installed, click Start, click Run, type adsiedit.msc in the Open box, and then click OK.
Right-click ADSI Edit, and then click Connect to.
Under Connection Point, click Select a well known Naming Context, and then make sure that Default naming context is selected in the drop-down box.
In the navigation pane on the left side, in the AD DS hierarchy, locate the mail-enabled group that isn't synced to Office 365. Right-click the group, and then click Properties.
Click Filter, and then clear the Show only attributes that have values option.
On the Attribute Editor tab, locate the displayName attribute, and then double-click it.
In this example, the value of the displayName attribute is set to <not set>. This is reason why the group isn't synced to Office 365.
In the Value box, enter a display name for the group, and then click OK.
Exit ADSI Edit.
Set the value of the FullSyncNeeded registry entry to 1. To do this, follow these steps:
Open Registry Editor. To do this, click Start, click Run, type regedit, and then press Enter.
In Registry Editor, locate the following registry subkey: