Unable to sign in to newly created Microsoft 365 tenant – admin account not recognised after domain setup

Hi @Bhavesh Patel,

Welcome to Microsoft Q&A forum.  

Thank you for providing such a clear and detailed explanation of the situation. I understand how critical this is, particularly given that this is a newly created Microsoft 365 tenant and there are currently no other global administrators able to sign in.

Based on what you described, I’d like to clarify an important and commonly overlooked behavior that can occur during custom domain configuration in a new Microsoft 365 tenant.

Once your custom domain has been added and successfully verified, and your username is updated to use the custom domain instead of the default @onmicrosoft.com domain, your sign‑in address will change.  For example, your username can be updated from ******@onmicrosoft.com to ******@customdomain.com. After this change, the system will automatically sign you out, and you will need to sign back in using the new username with the same password. This is expected behavior and does not indicate that the admin account was deleted or lost.

After the sign‑out, the original @onmicrosoft.com username may no longer be valid for authentication, which can give the impression that the admin account no longer exists.

Please try the following steps carefully:

1. Go to https://admin.microsoft.com
2. Sign in using the updated admin username with the custom domain, for example: ******@customdomain.com
3. Use the same password you originally set for the admin account.
4. If sign‑in is successful, you should regain access to:
   • Microsoft 365 Admin Center
     • Exchange Online

If you are unable to sign in using the updated username with the custom domain, the next step is to contact Microsoft Support directly through Customer service phone numbers - Microsoft Support or create a ticket via Contact Us - Microsoft Support so they can assist with verifying or restoring administrator access.

I hope this information helps. Please try the steps and let me know whether they resolve the issue. If the problem persists, we can work together to find a solution. 

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To recover access to your newly created Microsoft 365 tenant where the admin account is not recognized, you can follow these steps:

1. Confirm Account Details: Ensure you are using the correct email address that was set as the admin account during the tenant creation. Sometimes, a typo or incorrect email can lead to sign-in issues.
2. Identity Verification: Since you mentioned that account recovery reports the account does not exist, you may need to verify your identity and ownership of the organization through Microsoft’s support channels. This may involve providing official business documentation or domain ownership verification.
3. Submit a Support Request: If you cannot access the admin account, you should submit a support request through the Microsoft 365 support page. Select the option for issues related to signing in or accessing your tenant. You may be asked to provide information to verify your identity.
4. Contact Microsoft Support: If you have no other global admins, you can reach out to Microsoft support directly for assistance. They can guide you through the recovery process, especially since this is a brand-new tenant.
5. Check with IT Partner: If you had an IT partner set up the tenant, contact them for support as they may have additional access or insights into the setup process.

Since this is a new tenant, it’s crucial to act quickly to recover access before any further complications arise.

References:

• Tenant access recovery
• Troubleshoot sign-in issues and account access problems