add domain to Microsoft Admin

Question

I wanted to add my professional domain (oscarconfecoes.pt) to Microsoft Admin.

After adding the TXT record, a message appeared stating that my professional domain has already been added to another Microsoft 365 organization that I don't recognize.

My organization is associated with oscarconfecoes.onmicrosoft.com, and my professional domain was added to oscarconfecoespt.onmicrosoft.com, which I don't recognize.

How can I solve this?

Thank you

Answer 1

Hello @Jorge Silva,

Good day! I hope your doing well.

Based on your description, the issue occurs because your custom domain is already associated with another Microsoft 365 tenant. A custom domain can only be linked to one Microsoft 365 organization at a time, so it cannot be added to your current tenant until it has been released from the other one.

As this involves ownership validation and backend domain association, it requires a deeper investigation by Microsoft’s internal teams. We recommend reaching out to the Microsoft Technical Support Team for further assistance.

Their specialists can verify domain ownership (typically via DNS records) and, if needed, escalate the case to the appropriate team to help release the domain from the other tenant.

For Business support:   

• Find your Microsoft 365 admin: If you don't know who the global admin is in your organization, you can find guidance here: How can I find my Microsoft 365 admin? - Microsoft Support    
• Submit a service request: The Global Administrator should create a support request with Microsoft to receive advanced technical assistance. For detailed instructions, see: Get support - Microsoft 365 admin | Microsoft Learn    
• If your organization's subscription is from a partner or reseller, contact the reseller's support provider to help open a service request on behalf of you instead.    

When contacting support, it is helpful to clearly mention that:

• You own the custom domain
• The domain is already attached to an unknown or inaccessible tenant
• You would like Microsoft to help release or transfer the domain so it can be added to your correct tenant

I sincerely apologize for redirecting you to the Microsoft Technical Support Team. While I strive to assist as much as possible here in the forum, my capabilities are limited when it comes to backend-level checks, domain ownership verification, and tenant-level operations. These scenarios require access to internal tools that only the official support team can provide.

If you need further assistance or help refining your support request, please feel free to reply - I’ll be happy to assist.

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Answer 2

The custom domain can only exist in one Microsoft 365 organization at a time. The error indicates that oscarconfecoes.pt is already verified in another tenant (oscarconfecoespt.onmicrosoft.com), so it cannot be added to oscarconfecoes.onmicrosoft.com until it is removed from the first tenant.

To resolve this:

1. If that other tenant belongs to the same organization and there is admin access to it:
   • Sign in to the Microsoft 365 admin center of oscarconfecoespt.onmicrosoft.com as a global admin.
   • Go to Settings → Domains.
   • Select oscarconfecoes.pt and remove it from that tenant.
   • After removal completes, go back to oscarconfecoes.onmicrosoft.com and add/verify oscarconfecoes.pt again by following the normal domain-add process (TXT/MX verification as already started).
2. If that other tenant is unknown or there is no admin access to it:
   • The domain is in use by another Microsoft 365 organization. In this case, self-service removal is not possible.
   • Contact Microsoft 365 Support from the tenant where the domain should be used (oscarconfecoes.onmicrosoft.com):
     • Sign in to the Microsoft 365 admin center.
     • Select Help & Support in the lower-right corner.
     • Describe the issue (for example, “Custom domain already added to another Microsoft 365 organization that I don’t recognize”).
     • Work with support to prove ownership of oscarconfecoes.pt (typically via DNS records) and request that the domain be released from the unknown tenant so it can be added to the correct one.

The key requirement is that oscarconfecoes.pt must be removed from the other Microsoft 365 organization before it can be verified and used in oscarconfecoes.onmicrosoft.com.

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References:

• Error message when you try to verify a domain in Office 365
• Add a custom domain to Microsoft 365
• Add a custom domain name