Issue with SMS authentication (Error Code: 399287)

Question

Dear Microsoft Support Team,

I encountered an issue with SMS authentication. My tenant can not authenticate with SMS and show the error in bellow.

My phone number is normal authentication with other tenant.

My tenant ID: [Moderator note: personal info removed]@mon112.onmicrosoft.com

Please help me to resolve this issue because it is urgent

Error Code: 399287

Request Id: [Moderator note: personal info removed]

Correlation Id: [Moderator note: personal info removed]

Timestamp: 2026-04-01T13:04:25Z

Answer 1

Dear @Khoa Vương Đăng,

Good day! Welcome to Microsoft Q&A forum!

Based on your description, I understand that you’re experiencing an issue where SMS authentication is failing for your tenant, even though your phone number works normally with SMS authentication in other tenants. You’re seeking assistance resolving this urgent problem, as attempts to authenticate result in Error Code 399287 along with the associated request and correlation IDs.

The error code usually indicates that the issue may be related to your phone number used for SMS-based two-factor authentication (2FA) being flagged as having a poor reputation. This can sometimes occur after multiple login attempts in a short period, particularly if those attempts were unsuccessful.

• May I ask if you are the only Admin or there are other Admins in your organization?

If you're an admin, please check to see if there are other IT admins in your organization who can help you with the Multi-Factor Authentication (MFA) reset following this article: Manage user authentication methods for Microsoft Entra multifactor authentication

If you're the only admin, in this situation, the Microsoft Data Protection Team has tools and processes in place to verify identity and regain access to administrator accounts. 

Please note that this is a community forum where users help one another. We do not have control over user accounts, including login issues, password resets, or access changes.

Therefore, if you are the only administrator in your organization, then you need to involve Microsoft Data Protection Team. Please try to find the related hotline number to call the frontline let them raise a ticket for you: Customer service phone numbers - Microsoft Support (Scroll down for Business users) 

In some countries, this is an automated conversation: First, when you call the hotline, they will ask you what kind of problem you are struggling with. 

Answer: Authenticator. 

A: What products do you use? 

B: Office 365 for business. 

Verification: Education or company account? 

B: For companies 

A: Are you an administrator? 

B: Yes. 

A: Are there any other administrators in your organization? 

B: No. 

A: I need one.... Service request? 

B: Yes 

(Important Note: Sometimes, you would hear the computer-generated voice at first, please kindly wait for it to end, and if an agent is available, you would be directed to them and get your support. Depending on your country or region, 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.)

As an alternative, you can create a new tenant account and submit your request from there.    

To set up a new tenant, please follow these steps: 

• Visit Compare Office 365 Enterprise Pricing and Plans | Microsoft 365, choose any plan and click try for free to start a free trial.    
• Follow the guided setup process to create a new account for a new tenant. 

Once your tenant is created, you should be able to access the support portal and submit your ticket referencing your locked account without further issues.

In the ticket's subscription, you could refer to this message "Hello,

I’m unable to access my Administrator account. While my password works, Microsoft isn’t sending the SMS verification because the account shows as ‘not verified.’ I also can’t reach support since it requires logging into the same Admin account.

To resolve this, I have created a new tenant and would like to be connected with the Data Protection team to verify my identity and assist with regaining access. I am available to provide any required documentation or verification to support the recovery process."

Ticket Support: In the Microsoft 365 Admin Center > Support > Help & Support. You can raise support ticket at: https://admin.microsoft.com/#/support/requests   

Please remember to cancel the trial subscription once your issue is resolved to avoid any unintended charges.

Thank you for your kindness and patience!

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Answer 2

Error 399287 indicates that Microsoft Entra ID has blocked the phone number for SMS verification due to a “bad reputation” or similar protection logic on Microsoft’s side. This is not something that can be fixed from the tenant portal or by changing user settings.

Key points from similar resolved cases:

1. When a number is flagged with bad reputation, SMS MFA for that number in that tenant stops working and returns error 399287.
2. The fix requires Microsoft support (specifically the Microsoft 365/Microsoft Data Protection team) to reset or clear the MFA state/phone reputation on the backend.

Recommended actions:

1. Open a support case with Microsoft
   • If there is at least one Global Administrator who can still sign in, that admin should open a support ticket from the Microsoft 365 or Azure portal and include:
     • Error code: 399287
     • Request ID, Correlation ID, Timestamp
     • A description that SMS verification is blocked for the phone number due to bad reputation.
   • Ask support to involve the Microsoft Data Protection team to reset MFA / clear the block on the phone number. This is how similar cases were resolved.
2. If locked out and no other admin can sign in
   • If this is the only admin account and it cannot pass MFA, contact Microsoft support by phone and request escalation to the Data Protection team for MFA reset and identity verification, as described in the referenced guidance.
   • If direct access to support is not possible from the affected tenant, create a temporary Microsoft 365 trial tenant, go to the Admin Center → Support → Help & support, and open a ticket clearly stating that the issue is with a different existing tenant where the admin is locked out and SMS MFA returns error 399287.
3. Do not keep retrying SMS excessively
   • Excessive or repetitive verification attempts can contribute to blocking. Wait for support to clear the block instead of repeatedly requesting new SMS codes.

The actual unblock/reset of the phone number and MFA configuration can only be completed by Microsoft support; tenant configuration changes alone will not remove the 399287 bad-reputation block.

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References:

• Troubleshoot Microsoft verification code issues
• Common problems with two-step verification for a work or school account
• 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
• I need to reset my mfa methods - Microsoft Q&A