Add Alias Exchange Online
In a synchronized environment, when you try to add or remove aliases on an Office 365 mailbox from the admin console, you’ll get an error like this :
The operation on mailbox “Dumbo” failed because it’s out of the current user’s write scope. The action ‘Set-Mailbox’, ‘EmailAddresses’, can’t be performed on the object ‘Dumbo’ because the object is being synchronized from your on-premises organization. This action should be performed on the object in your on-premises organization.
When you sync your users, the identity reference is your Active Directory, that’s why you need to edit your local Active Directory domain to modify your mailboxes on Office 365.
For managing mailboxes aliases, you need to edit the “ProxyAddresses” attribute :
In this attribute, you can set the aliases and the Primary SMTP address with some naming convention to respect.
To add an alias, you need to add the email address prefix with “smtp:”, the case matter. You can add a bunch of them.
Primary SMTP :
To set the primary SMTP address, you need to add the email address prefixed with “SMTP:”, once again, case matter, and only one can be set, indeed, this is the default sending mail address.
Add Alias Exchange Online – Example :
Take our test user, Dumbo, in local Active Directory :
In Exchange Online :
Now, let’s modify this in our Active Directory :
Let’s check in Exchange Online :
And voilà, the primary SMTP address and aliases changed to the specified value in the local Active Directory. Of course, for the modification to take effect, you need to wait/trigger an AADCoonect synchronization, plus a few minutes for letting Office 365 process the changes.
Note : You can trigger a sync in some different ways depending of the sync tool you use :
This changes happen without affecting the Outlook/mobile devices connected to the mailboxes you modify.