Issue with Syncing the new "onmicrosoft.com" Fallback Domain as Alias in Azure AD Connect

[janakkhadka]

Hello Team,

I am experiencing an issue with Azure AD Connect in my hybrid environment. I have recently added a new onmicrosoft.com domain to my Microsoft 365 tenant, and made Fallback domain. I want to add this domain as an email alias for my users/groups. However, I am unable to sync this new domain as an alias for my Azure AD synced users. Here are the steps I have taken:

1. I added the new onmicrosoft.com domain to my Microsoft 365 tenant.
2. I updated the ProxyAddresses attribute for my on-premises Active Directory users to include the new onmicrosoft.com domain as an alias.
3. I ran a manual sync using Azure AD Connect.
Despite these steps, the new onmicrosoft.com domain is not appearing as an alias for my users in Microsoft 365. I understand that the onmicrosoft.com domain is typically used as a fallback domain and is not usually included in the Azure AD Connect synchronization. However, I would like to use this domain as an alias for my users and groups as we are in the process of rebranding our organization. Could you please assist me in resolving this issue? Any help would be greatly appreciated.

Thank you,
Janak Khadka

[#2]

@janakkhadka 

Not quite understand your situation, onmicrosoft.com supposed to be added by default without any action

[#3]

In case of company rebranding, there is the provision of adding an extra ‘onmicrosoft.com’ domain within the same Tenant and make it the fallback domain. I’m surprised that you don’t know about it.