Emails are being sent from onmicrosoft.com instead of the company's domain

Question

I'm experiencing an issue with Exchange Online.

After changing a user's license from Microsoft 365 Business Premium to Microsoft 365 E5, the user started sending emails using the onmicrosoft.com domain instead of the company's custom domain. So far, I have migrated the licenses of 10 users, but this issue has only occurred with this specific account.

We have an on-premises Active Directory synchronized with Microsoft 365. The UPN and directory synchronization are working correctly.

No configuration changes were made that could have caused this issue—only the license change. Even so, I compared this user's settings with other users who are working correctly and couldn't find anything disabled or configured differently.

Additional observation: When I click on the user's name to view their contact details, both the onmicrosoft.com email address and the company's email address are displayed. For the users who are working correctly, only the company's email address is shown.

Has anyone experienced this issue before or knows how to resolve it?

Answer 1

Hi Raul
Thank you for reaching out. 

From your description, this appears more likely to be related to the affected user's email address configuration rather than the license change itself, especially since the same migration was performed for multiple users and only one account is affected. 

As far as I know, in a directory-synchronized environment, Exchange Online relies on the email address attributes synchronized from on-premises Active Directory. A license reassignment may trigger mailbox reprovisioning or re-evaluation of mailbox attributes, which could expose an existing issue with the user's SMTP address configuration. 

Since the affected user is sending from the onmicrosoft.com address and the contact card displays both the custom domain address and the onmicrosoft.com address, I would recommend verifying whether the correct company address is configured as the Primary SMTP address and checking the user's synchronized email attributes. 

You could try to run the following command in Exchange Online PowerShell: 

Get-Mailbox "identity" | Format-List PrimarySmtpAddress,WindowsEmailAddress,EmailAddresses,EmailAddressPolicyEnabled,IsExchangeCloudManaged

You can also check the user’s proxyAddresses attribute in on-premises Active Directory (Attribute Editor). 

In order to better assist you, I will open a private message within this thread. Please share the output of your AD attributes from your side so I can better understand the issue. This approach helps to protect your personal information and prevents sensitive information from becoming publicly visible.

To view or send private messages, please sign in to the Microsoft Q&A forum with the account that was used to create this thread, and then select "Private messages" 

 

Any updates would be greatly appreciated. 

Please understand that our initial reply may not always immediately resolve the issue. However, with your help and more detailed information, we can work together to find a solution.  

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