Error Code: 399287

Question

Unable to Verify Identity for Azure Login – Error 399287

I can successfully sign in to my Microsoft account, but then, I'm prompted to verify my identity. However, when I do SMS verification, I receive the following error message:

Error Code: 399287

I'm aware that this is a known problem with SMS, and "bad reputation" for phone number.

And no other options for MFA is offered.

Answer 1

Hello Jason,

I have reached out to the engineering team to unblock MFA for your account. They have now unblocked it from the backend and removed the bad reputation on it. You should be able to log in to the Azure Portal without any issues.

Please try logging in and check if you can complete SMS authentication without any errors. Let me know if you encounter any issues.

I hope this information is helpful. Please feel free to reach out if you have any further questions.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment". Thanks

Answer 2

Error 399287 indicates that Azure has blocked the phone number for SMS verification because it has been flagged with a “bad reputation.” When this happens, SMS-based MFA for that number will fail and, in some reported cases, no alternative MFA options are presented.

This block cannot be cleared from the user side. The resolution requires Microsoft support to reset or clear the MFA configuration/phone reputation on the backend. In similar cases, the Microsoft 365 Data Protection team has reset MFA and removed the block so that sign-in can proceed.

Action steps:

1. Contact Microsoft support and request involvement of the Microsoft 365 Data Protection team, explaining that:
   • Sign-in succeeds with username and password.
   • SMS verification fails with Error Code 399287.
   • The phone number appears to be blocked due to “bad reputation.”
   • No other MFA methods are available.
2. If this is a work/school (Microsoft 365 business/education) account and there is at least one other global admin, that admin can open a support ticket from the Microsoft 365 admin center on behalf of the affected user.
3. If this is the only admin account in the tenant and access to the admin center is blocked, follow the pattern used in similar locked-out-admin scenarios:
   • Call the regional Microsoft support hotline and state that the issue is with “Authenticator/MFA” for an Office 365 for business (work/school) account and that this is the only administrator.
   • Ask the frontline agent to open a service request and route it to the Data Protection team to reset MFA / clear the phone number block.
   • Be prepared to provide tenant and account details and complete identity verification.
4. If direct access to support is not possible (for example, subscription through a partner), contact the reseller/partner and ask them to open a Microsoft support ticket for this issue.

Once the Data Protection team resets MFA and removes the block, sign-in with SMS or with newly configured MFA methods should work again.

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References:

• 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