Using ADSIedit to Add or Remove E-mail aliases on on-Premises Active Directory

If you are synchronising your Office 365 account with your on-premises exchange/Active Directory, you will know that you cannot edit exchange user properties using the Office 365 administrator portal.

If you try, you will come across this error or a similar one:

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

In this article, you can know how to add e-mail aliases using the Active Directory Service Interfaces Editor (adsiedit).

Step-by-step guide

1. Go to Start > Run and type adsiedit.msc
2. Now, find the unit where your AD user’s reside (for example: Fabricam - Office-RU-SPB)
3. Right click the user you want to edit and click Properties.
4. Find the variable proxyAddresses – this is the one you want to edit. 
   When you add new e-mail aliases, you need to make sure that your primary e-mail address will start with upper-case SMTP. Your aliases -  secondary addresses should be lower-case smtp. For example: 
   In the proxyAddresses attribute, you need put:
   SMTP:firstnamelastname@domain.com - Primary address
   smtp:firstnamelastname@domain.com  - alias, aka secondary address