MFA when signing in: cannot receive code by SMS - error 399287

Question

Hello,

When I try to sign into my Microsoft 365 account, I am unable to verify my identity because no SMS can be sent to my mobile phone number. I get error 399287. There is no other way to sign in offered.

I understand that this is because my mobile phone number is seen as having a bad reputation which I don't understand - it's been my number for years, never used in any other usage than a personal usage.

Would it be possible to unlock this phone number?

Answer 1

There is no other MFA method associated to this account. I must rely to SMS to sign into this account. This has already become problematic because I am not able to renew my payment method.

Answer 2

When you encounter error 399287 while trying to sign into your Microsoft 365 account, it indicates that your mobile phone number has been flagged for having a "bad reputation". This can prevent SMS verification codes from being sent to your device. Unfortunately, the resolution for this issue typically involves contacting Microsoft support, as they can assist in removing the flag from your phone number.

Here are a few steps you can consider:

1. Contact Microsoft Support: Reach out to Microsoft support for assistance in removing the bad reputation flag from your phone number. They may require some verification details from you.
2. Alternative Verification Methods: If available, check if you can use other methods for multi-factor authentication (MFA), such as using the Microsoft Authenticator app or receiving a verification call instead of an SMS.
3. Check Account Settings: Ensure that your phone number is correctly listed in your account settings, as incorrect information can also lead to verification issues.

It's important to resolve this with Microsoft support to regain access to your account securely.

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References:

• Unable to Verify Identity for Azure Login – Error 399287
• Azure has blocked my phone number for SMS verification due to a “bad reputation” flag