unable to add additional email address

Question

unable to add additional email address

Glenn Maxwell 12,456

Hi All,

I am using an Exchange 2016 hybrid environment. We create users on-prem and then migrate them to Exchange Online. I have a user, ******@contoso.com, and I want to add an additional email address, ******@contoso.com, to this user. When I execute the following command in both Exchange On-Prem and Exchange Online, I encounter these errors:

Exchange On-Prem:

Set-Mailbox ******@contoso.com -EmailAddresses @{add = "******@contoso.com" }

Error: The operation couldn't be performed because object '******@contoso.com' couldn't be found on '******@contoso.com'.

Exchange Online:

Set-Mailbox ******@contoso.com -EmailAddresses @{add = "******@contoso.com" }

Error: The operation on mailbox "10d1a7ccc-7j8i-ki98-7jio-89lknh667654" failed because it's out of the current user's write scope. The action 'Set-Mailbox', 'EmailAddresses', can't be performed on the  object '10d1a7ccc-7j8i-ki98-7jio-89lknh667654' because the object is being synchronized from your on-premises organization. This action should be performed on the object in your on-premises organization.

Bruce Jing-MSFT 10,155 Reputation points Microsoft External Staff

2025-03-11T06:27:33.76+00:00

Hello, @Glenn Maxwell

It's been a long time since I've heard from you, have you solved your problem yet? Did my previous reply help you？ If it was useful, you can mark it as an answer. Thank you for your understanding and support.

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Bruce Jing-MSFT 10,155 Reputation points Microsoft External Staff

2025-03-11T06:27:33.76+00:00

Hello, @Glenn Maxwell

It's been a long time since I've heard from you, have you solved your problem yet? Did my previous reply help you？ If it was useful, you can mark it as an answer. Thank you for your understanding and support.

Answer 1

Hi,@Glenn Maxwell

Thanks for posting your question in the Microsoft Q&A forum.Based on the information you provided, you create a user in On-pre and then migrate him to Online.

To add an email address to a user mailbox in a hybrid environment, you typically need to make the change on the on-premises Active Directory, and then let Azure AD Connect sync the change to Office 365.

Here are the steps you should follow:

1.Open Active Directory Users and Computers and locate the user account (******@contoso.com).

2.Edit the ProxyAddresses Attribute

3.Force Azure AD Connect Synchronization

4.Verify the Changes in Exchange Online

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unable to add additional email address

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