Can not install Outlook for my business email on my new Samsung S25 Ultra, Microsoft has apparently blocked me and no authenticator will work on this phone either.

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Hi Michael Holmes

Thank you for reaching out to Microsoft Q&A Forum and sharing your experience.

I understand your frustration after spending hours troubleshooting this on your new S25 Ultra.

The fact that your email functions correctly on your Surface Pros indicates that your account remains active.

The 500121 error specifically indicates a failure in the Multi-Factor Authentication handshake. For security purposes, Microsoft Authenticator tokens do not automatically transfer to new hardware. The quickest way to restore access is to contact your organization's IT Administrator and ask them to follow this official Microsoft guide to reset your multi-factor authentication (MFA) settings.

If you are the only global admin, the correct procedure for your situation is to contact the Microsoft 365 Data Protection team. You can reach them directly by phone using the numbers listed here: Customer service phone numbers - Microsoft Support

In case this phone line is not supportive, you can consider directly submitting a support request as a helpful workaround: Go to Microsoft 365 Business Plans and Pricing and click Try for free to set up a temporary Microsoft 365 tenant with a trial license. Use this new account to sign in to the Microsoft 365 Admin Center and submit a support request on behalf of your primary account. For further instructions, you can follow this guide: Get support - Microsoft 365 admin | Microsoft Learn

Note: This method doesn't require you to use your new account for your business. Instead, it allows you to create a temporary global administrator account so you can submit a support request. The trial account is free for one month. Be sure to delete it after submitting your support request to avoid any automatic renewals or charges from Microsoft.

Please note that this process will take more time than usual (7-14 working days) for your account to get access again as Microsoft's Data Protection team is always overwhelmed with the number of tickets. As a forum moderator, I do not have access to Microsoft internal system to assist or push this process to be quicker.

I hope my information is helpful. Please give me any updates once you get this resolved.

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