Hello @陈晨,
Thank you for reaching out to the Q&A forum!
To make sure we correctly identify your situation and avoid any misunderstanding, please provide me more detail:
1.Where and how did you register your domain?
2.Could you share a screenshot or the exact error message you see when trying to add the domain to your Microsoft 365 tenant?
Specifically, any message indicating that the domain is already associated with another Microsoft 365 organization.
Note: I can help you blur or hide any personal information if needed.
The reason I’m asking is that when I performed a tenant lookup for your domain across all three regions through Tenant Lookup, I couldn’t find any active tenant linked to it.
I am thinking that the domain might be associated with an unmanaged tenant (a tenant created when someone signed up for Microsoft services using an email from your domain, without setting up a full organization).
Issues related to domain setup or configuration in Microsoft 365 can be complex and involve strict security protections, so, I hope you understand why I need these details to help you effectively.
Looking forward to hearing from you.
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