MFA & Verification Issues

How to Fix Microsoft Phone MFA Blocked by PhoneReputation (Error 399287)

John Wilson Sep 29, 2026 870 views

Question details

The user is unable to sign in to their account because their phone multifactor authentication (MFA) has been restricted.

How to Fix Microsoft Phone MFA Blocked by PhoneReputation (Error 399287)

Product: Microsoft Account
Device & OS: not provided
Scenario: Attempting to sign in using phone call or SMS multifactor authentication.
Observed behavior: The authentication request is blocked by PhoneReputation, returning error code 399287 and preventing account access.

Before you start

Stop requesting new SMS codes immediately to prevent extending the temporary block on your phone number.

Solution 1Recommended

Contact Your IT Administrator (For Work or School Accounts)

If you are using an organization-managed account, your IT admin has the necessary tools to reset your authentication methods and bypass the block.

End users cannot unblock their own phone numbers once they are flagged by the PhoneReputation system. Only an administrator with access to the Microsoft Entra admin center can resolve this.

Reach out to IT Support

Contact your organization's IT support desk or system administrator through an alternative communication channel like email or an internal ticketing system.

Request MFA revocation

Ask the administrator to revoke your currently blocked phone number from your user account's authentication methods.

Re-register authentication

Request the administrator to trigger the 'Require re-register MFA' option so you can set up a new method, such as the Microsoft Authenticator app.

Contact Your IT Administrator (For Work or School Accounts)

Use Authenticator Apps: Once your access is restored, it is highly recommended to set up an authenticator app instead of relying solely on SMS, as it is more secure and avoids telecom carrier delivery issues.

Solution 2

Contact Microsoft Data Protection Support (For Admin Accounts)

If you are the sole global administrator for your Microsoft tenant and are locked out, you must contact Microsoft directly for account recovery.

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Frequently Asked Questions

What does error code 399287 mean in Microsoft authentication?

Error code 399287 indicates that your phone number has been flagged by Microsoft's PhoneReputation system. This temporarily blocks the number from receiving SMS or voice calls for multifactor authentication due to unusual activity, such as too many request attempts.

Can I unblock my phone number from PhoneReputation myself?

No, end users cannot directly unblock phone numbers restricted by the PhoneReputation system. You must contact your IT administrator to reset your MFA methods, or contact Microsoft Support if you are the sole administrator.

How can I prevent my phone number from being blocked for MFA in the future?

Avoid repeatedly clicking 'Resend code' if SMS messages are delayed. To prevent SMS-related blocks entirely, switch to using an authenticator app (like Microsoft Authenticator or Google Authenticator) as your primary verification method.

Login & Account Issues