unable to rename smtp address having onmicrosoft.com

Question

Hi All

I am using exchange 2010 hybrid environment, we create regular mailboxes and shared mailboxes in onprem and migrate them to cloud.
i have a shared mailbox with name sharedmailbox01@Company portal .com, i have renamed it to sharedmailbox@Company portal .com in onprem, but in cloud
still i am still seeing secondary smtp address as sharedmailbox01@Company portal .onmicrosoft.com how do i delete this smtp address.
When i try to delete it from office365 exchange admin center i am getting the below error.

Answer 1

If you offboard the shared mailbox back to on-prem, then remove the Azure object and resync with AADConnect, that would work and clean that up.
This assumes its not licensed and not using OneDrive etc...

https://learn.microsoft.com/en-us/exchange/hybrid-deployment/move-mailboxes#move-exchange-online-mailboxes-to-the-on-premises-organization

Once the mailbox is moved on-prem, run this using connect-msolservice against the Azure sycned object to remove it

https://learn.microsoft.com/en-us/powershell/module/msonline/connect-msolservice?view=azureadps-1.0

https://learn.microsoft.com/en-us/powershell/module/msonline/remove-msoluser?view=azureadps-1.0

Remove-MsolUser -UserPrincipalName "sharedmailbox@contoso.com"  

Followed by:

Remove-MsolUser -UserPrincipalName "sharedmailbox@contoso.com" -RemoveFromRecycleBin  

Then Resync the object from on-prem and move the mailbox back to 365.

Answer 2

@Glenn Maxwell

It is an expected behavior for a migrated mailbox, you cannot remove the default email address(@keyman .onmicrosoft.com) from migrated mailbox.

You cannot see this email address with the command below, so you cannot remove it:

Get-RemoteMailbox Shared | fl EmailAddresses  

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