The built-in admin should not be mailbox enabled regardless, so I would disable the mailbox and there is no issue if you do.
Any drawbacks or consequences to disabling built-in administrator account mailbox (hybrid scenario)?
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Brian Hall
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Reputation points
We are looking to shut down (yes, we know not to uninstall) our last Exchange server after migrating all mailboxes to Microsoft 365, per this MS article:
https://learn.microsoft.com/en-us/exchange/manage-hybrid-exchange-recipients-with-management-tools
It mentions the following regarding built-in admin mailboxes:
By default, built-in admin mailboxes are not synced to the cloud by cloud sync or Microsoft Entra Connect. Before you proceed, you should disable these mailboxes using Disable-Mailbox.
Is there any potential negative impact to disabling the mailbox for the built-in administrator account if we do this? We don't use the account for communications.
Windows for business | Windows Client for IT Pros | Directory services | Active Directory
Microsoft 365 and Office | Install, redeem, activate | For business | Windows
Microsoft 365 and Office | Install, redeem, activate | For business | Windows
Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Exchange | Exchange Server | Management
Exchange | Exchange Server | Management
The administration and maintenance of Microsoft Exchange Server to ensure secure, reliable, and efficient email and collaboration services across an organization.
Exchange | Hybrid management
Exchange | Hybrid management
The administration of a hybrid deployment that connects on-premises Exchange Server with Exchange Online, enabling seamless integration and centralized control.
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Kai Yao 37,781 Reputation points Moderator2023-11-17T01:32:20.3366667+00:00 Hi @Brian Hall,
Just checking in to see if above information was helpful. Please let us know if you would like further assistance.
If the issue has been resolved, please accept the helpful replies as answers to help other community members.
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Andy David - MVP 159.7K Reputation points MVP Volunteer Moderator2023-11-13T20:16:37.99+00:00 -
Brian Hall 101 Reputation points
2023-11-20T12:59:43.0266667+00:00 Thank you Andy, I think the mailbox was auto created years ago when Exchange was installed for the first time.
I appreciate the info.
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Justin Emlay 0 Reputation points2025-12-30T16:38:01.0733333+00:00 Just to be absolutely clear, we're talking about this right?
Disable-Mailbox -Identity "Administrator"
Domain Administrator? And yes, this is created by default on the installation of Exchange. For us that would have been Exchange 2000.
I'm in the same boat. Hybrid, moving everything over. Down to the last few mailboxes trying to get this server in free mode with no mailboxes. AI was no help at all. It said if you delete the admin mailbox then you'll break your hybrid config. I think it confused mailbox with account.
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Brian Hall 101 Reputation points
2023-11-20T12:58:51.17+00:00 Thank you Andy, I appreciate the info.