Add SMTP Alias to Exchange Online User With AD Sync

In this blog post, I’ll show you how to add a new SMTP Alias to an Active Directory user with an Exchange Online mailbox when AD Sync installed.

If you try to add the Alias directly from Exchange Online you will receive the error below:

The operation on mailbox “Mailbox Name” failed because it’s out of the current user’s write scope. The action ‘Set-Mailbox’, ‘EmailAddresses’, can’t be performed on the object ‘Object Name’ because the object is being synchronized from your on-premises organization. This action should be performed on the object in your on-premises organization.

The reason for the error Is because we have AD Sync configured and therefore all changes must be applied from Active Directory and Sync to Office 365 Exchange Online.

In this we need to add the Alias from Active Directory, To add an SMTP alias we need to use the Active Directory Console or Active Directory Administrative Center.

I recommend using Active Directory Administrative Center

From the Administrative Console search for the user and open the properties -> Extensions

Click Attribute Editor and search for ProxyAddresses

In the ProxyAddresses filed add an SMTP Alias, type the address In the following format.

Note: To make the Alias the Primary SMTP Address use capital SMTP like the example below:

Wait for AD Sync and you’re done.

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