Unable to Verify Identity for Microsoft 365 Login – Error 399287

Question

Unable to Verify Identity for Microsoft 365 Login – Error 399287

Answer 1

Hello @Pedro Pina,

Thank you for sharing the error message.

The error 399287 when attempting to verify identity by SMS during Microsoft 365 sign‑in usually indicates that Azure has flagged the phone number as having a “bad reputation”. When this happens, Microsoft blocks the number from being used for SMS‑based verification as a security measure. Unfortunately, this block cannot be removed by the end user.

In this situation, the recommended next step depends on your role in the organization.

 

If you are an end user, please contact your IT administrator and ask them to reset your MFA settings or require MFA re‑registration for your account. They can following these steps: 

• Signing in to the Microsoft Entra Admin Center
• Navigating to Users > Your Account > Authentication methods  
• Selecting Require re-register MFA  

If you are the only administrator (Global Admin) in the tenant and cannot sign in due to this error, you will need to contact Microsoft’s Data Protection team. This team has the authority and the specific security procedures to verify your identity as the legitimate owner of the account and then reset your MFA settings from their end. Please try to find the related hotline number to call the frontline and let them raise a ticket for you: Customer service phone numbers - Microsoft Support    

Here are some tips and an example of a prompt to help you navigate the IVR more effectively:  

(When you call the support number, you may hear an introduction of about 30 seconds such as "you can visit the link...". You can ignore this introduction and wait until you are presented with the options. Then press "1" as a business email user, and again "1" for technical help.)    

In some regions, the initial interaction may be automated, so here’s a general idea of how the conversation might go to help you prepare:      

• What kind of problem are you experiencing?         
• Answer: Authenticator         
• What products do you use?         
• Answer: Office 365 for business         
• Is this for an education or company account?         
• Answer: For companies         
• Are you an administrator?         
• Answer: Yes         
• Are there any other administrators in your organization?         
• Answer: No. I am the only admin in my tenant          
• Do you need a... Service request?          
• Answer: Yes. I need to create a ticket. Please send me direct to the Data Protection Teams.      

During the phone call, you will need to provide the information associated with your subscription, such as your company name, billing details, phone number, and an alternate email address, etc. This information allows the Data Protection team to verify your identity and securely assist you in regaining access to your administrator account. 

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If you are unable to reach support via the phone numbers, there is a workaround you might consider: You can register for a new Microsoft 365 tenant by signing up for a trial subscription here: Microsoft 365 Business Plans and Pricing | Microsoft 365    

Once the new tenant is created, you can access the admin center and submit a support ticket from there, requesting to speak with the Data Protection Team on behalf of your original tenant.    

Important notes:     

• This new trial tenant will not give you access to any of the data or settings in your original locked tenant. It is solely a temporary means to contact Microsoft support.    
• The resolution time might be longer as you are contacting support from a different tenant.    
• Remember to cancel the trial subscription for the new tenant once your issue with the original account is resolved to avoid any unintended charges.  

I hope the information provided helps guide you in the right direction. Although I’m unable to take direct action, I sincerely hope that the steps and recommendations I’ve shared can support you through the process.  

  

Warm regards, 

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Answer 2

Error 399287 when trying to verify identity by SMS for Microsoft 365 sign-in typically indicates that Azure has flagged the phone number with a “bad reputation” and blocked it for SMS verification.

Because the number is blocked at the service level, this cannot be fixed from the user side (changing devices, retrying codes, or re-adding the number will not resolve it). The resolution requires Microsoft support to reset MFA/clear the block.

Recommended actions:

1. If this is a work/school (Microsoft 365 business/education) account and there is another admin in the tenant:
   • Contact the tenant administrator.
   • The admin should open a support ticket with Microsoft 365/Azure support and request:
     • MFA reset for the affected account, and
     • Removal of the “bad reputation”/block on the phone number used for SMS.
   • After Microsoft completes the reset, sign in again and reconfigure MFA with a working method (Microsoft Authenticator app is recommended over SMS).
2. If this is a work/school account and the affected user is the only admin:
   • Call Microsoft support using the regional “Customer service phone numbers - Microsoft Support” entry.
   • When prompted, clearly state that this is an Authenticator/MFA issue for an Office 365 for business account, that this is a company account, and that there are no other admins.
   • Ask to open a service request with the Microsoft Data Protection team to:
     • Verify identity as the tenant admin, and
     • Reset MFA / clear the phone-number block (error 399287).
   • Be prepared to provide tenant-identifying details (tenant name, domain, admin UPN, error code, timestamps) as requested by support.
3. If this is a personal Microsoft account (Outlook.com, Hotmail, etc.):
   • Use any available alternative verification method (backup email, other phone, or Microsoft Authenticator) if configured.
   • If no alternative method works and SMS is blocked, contact Microsoft consumer support and follow their identity verification flow; the same “bad reputation” block must be cleared by Microsoft.

In all cases, once access is restored, configure at least two MFA methods (for example, Microsoft Authenticator plus a backup phone or email) to avoid lockout if one method fails.

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References:

• Error Code: 399287 - Microsoft Q&A Unable to Verify Identity for Azure Login – Error 399287
• Azure has blocked myphone number for SMS verification due to a “bad reputation” flag - Microsoft Q&A
• I have a Micrsoft business account and I am the admin and the only user registered under this account. I can't log in because i have replaced my phone and the authenticator doesn't work. - Microsoft Q&A
• Microsoft authenticator sending me into a spiral - Microsoft Q&A