Unable to Verify Identity for Azure Login – Error 399287

Error 399287 is associated with a phone number being blocked for SMS verification because it has been flagged with a “bad reputation.” When this happens, SMS-based MFA for that number will consistently fail, and access to the tenant that relies on that method is effectively blocked.

For this situation, the resolution requires direct intervention from Microsoft support (Data Protection / Tenant Recovery / Microsoft 365 Data Protection team). Community forums and self-service options cannot remove the “bad reputation” flag or reset MFA for a locked-out tenant where no alternative verification method is available.

Use the following approach:

1. Engage Microsoft support (Data Protection team)
   • Contact Microsoft support by phone using the customer service phone numbers listed in the official support article “Customer service phone numbers - Microsoft Support.”
   • Clearly state that access to the Azure/Microsoft 365 tenant is blocked due to MFA issues and that SMS verification returns error 399287.
   • Indicate that this is a personal or single-admin tenant and there is no other administrator who can reset MFA.
   • The Data Protection team has tools and processes to verify identity and reset MFA or clear the block on the phone number, as reflected in similar resolved cases where “The Microsoft Data team has reset my MFA and solved the issue.”
2. If there is another global admin on the tenant
   • If any other global administrator exists on the tenant, that admin can sign in and reset MFA for the affected account:
     1. Sign in to the Azure portal and open Microsoft Entra ID.
     2. Go to Users and select the locked-out user account.
     3. Open Authentication methods and choose “Require re-register multifactor authentication.”
     4. After this, the next sign-in will prompt for fresh MFA registration, allowing configuration of a new method that works.
3. If truly the only admin and cannot sign in anywhere
   • Follow the pattern used in similar lockout cases:
     • Call Microsoft support using the global support phone numbers and request escalation to the Data Protection / Tenant Recovery team.
     • Be prepared to provide tenant details (tenant name/domain, billing information, proof of ownership) so they can verify identity and restore access.

Because the phone number is likely blocked at the service level (bad reputation), self-service retries or waiting will not resolve the issue. Resolution depends on Microsoft support resetting MFA and/or clearing the phone number block for the tenant.

References:

• Troubleshoot Microsoft verification code issues
• 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
• Global Admin Locked out - Microsoft Q&A
• Severity A Situation - Locked out of global admin account (MFA) - business down - Microsoft Q&A