Creating Custom attributes on On-Prem AD for Exchange Online users on O365

Creating Custom Attributes on On-Premises AD for Exchange Online Users

I have came across some interesting scenario where Exchange Server doesn’t exist however some attributes might be still required or used on Office 365 for Exchange online users which are Synced with Azure Active Directory Sync tool.

The attributes might be used for different purposes but sometimes it’s very necessary so I will go ahead and demonstrate how to create a custom attribute which is normally created by default with Exchange servers deployed on-prem.

First I will run the Schema console

On one of the DC servers which are synced with Office 365 Launch  CMD as Administrator

Run the following Command

regsvr32 schmMgmt.dll



Click on File -> ADD /Remove Snap in



Right Click on Attributes -> Create Attribute…



Click on Continue


Click OK

Go to Attributes, Navigate to Custom attributes and double click on it and tick the boxes below then click apply



Now go to Classes

Find and double click on User


Now go to Attributes tab


Click on Add and add the Custom Attribute



Click Apply

Now go back to CMD on DC Server and replicate changes across all DC servers


Open ADUC and check users attributes


Hope this helps  

7 thoughts on “Creating Custom attributes on On-Prem AD for Exchange Online users on O365”

  1. This is exactly my configuration and describes exactly what I’m trying to do. I want to populate the CustomAttribute1-15 attributes with information to be pulled by O365 for signatures. I’ve followed your instructions exactly and can see the attribute in AD, and can populate it. I’ve included it in the scope for the AD Sync, but I don’t see the values which are set in AD reflected in the Exchange properties of O365.

    The only difference I can see is that in O365, the attribute is “CustomAttribute1”, and in AD it’s “customAttribute1”. Is this case sensitive?

    1. In your case, You will need to set ADConnect in Hybrid mode so that the Exchange Online is set to accept values from On-premises.
      The O365 Exchange normally is locked unless you have Hybrid mode enabled.

    1. Hi Sebus,

      This is not the exchange ExtensionAttribute1 which you normally find on user’s attributes. it’s a custom attribute when you don’t have Exchange on-premises installed and Schema was not prepared so the ExtensionAttributes are not there.
      Instead of that I choose to create a custom attribute instead of extending AD schema with Exchange.

  2. Hi Thank you for this article, it works for me but with some changes,
    – My goal is to sync Custom Attribute from On-Premise AD to Exchange Online via O365, to create a Dynamic Distribution Groupe, with custom attribute rules.

    + The only difference is to change Custom Attribute X “Label” to Extension Attribute X “Label”.

    + MS AzureAD Connect | Refresh Directory Schema.
    + MS AzureAD Comnnect | Enable/Configure: Directory extension Attribute sync | add your Extension Attribute

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