Error 399287 – SMS MFA verification not working for Microsoft 365 account

Question

Error 399287 – SMS MFA verification not working for Microsoft 365 account

Giorgi Chelidze 0

Hello Microsoft Support Team,

I am a professor at Kutaisi International University in Georgia, using a university-provided Microsoft 365 account.

Until recently, I was able to sign in using SMS verification codes sent to my registered mobile phone. However, SMS authentication has stopped working.

Whenever I select SMS verification, I receive the following error:

Error Code: 399287

My phone number is still correctly registered in Microsoft Security Info, and SMS remains configured as my fallback authentication method.

I can successfully authenticate using the Outlook app on my tablet. However, I use a basic Nokia mobile phone and do not always carry my tablet, so SMS authentication is particularly important to me.

I understand that error 399287 may be related to Microsoft's phone reputation protection system (BadReputation).

Could a Microsoft support engineer please investigate whether my phone number has been incorrectly restricted and help restore SMS authentication?

I would especially appreciate a solution that does not require intervention from my university's IT administrator.

I can provide the Request ID, Correlation ID, timestamp, and registered phone number privately through a secure channel if needed.

Thank you for your assistance.

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2 answers

Your answer

Answer 1

Dear Giorgi Chelidze,

Thank you for providing the details. For security reasons, please do not post your phone number, Request ID, Correlation ID, or other sensitive information publicly in this forum.

Since this issue involves Multi-Factor Authentication (MFA) for a Microsoft 365 account that is managed by your university, there is unfortunately very little that I can do directly for an individual end user without involving the organization's administrators.

In a Microsoft 365 Education environment, MFA methods (including SMS verification) are managed by the organization's Microsoft Entra ID (Azure AD) administrators. If an MFA method becomes unavailable, stops receiving codes, or requires reconfiguration, the usual resolution is for the tenant administrator to:

Reset your MFA registration.
Remove and re-add your authentication methods.
Update or change your MFA configuration.
Review sign-in logs and authentication failures.
Escalate the issue to Microsoft Support if a backend service investigation is required.

While you mentioned that you would prefer a solution that does not require intervention from the university's IT department, MFA settings for a work or school account are controlled at the tenant level, so only your university's IT administrator has the necessary permissions to make changes or open a support case with Microsoft on your behalf.

Since you can still access the account through Outlook on your tablet, I recommend contacting the IT help desk at Kutaisi International University and explaining your situation.

You can also refer to this Microsoft support article for more information: Manage authentication methods - Microsoft Entra ID | Microsoft Learn

I hope this helps clarify the available path forward.

Answer 2

A university Microsoft 365 administrator must open the investigation because an end user cannot request a tenant telephony-policy change or backend phone-reputation unblock directly.

Error 399287 can occur when Microsoft’s telephony protections throttle or block an SMS transaction, but the error alone does not prove that the phone number has a permanent BadReputation restriction. Entra evaluates telecom requests using risk signals and may display “Sorry, we're having trouble verifying your account” when a transaction is flagged.^1^

What to ask university IT to do

Send IT the error details and ask them to take these actions:

Review a fresh failed sign-in
- Reproduce the problem with no more than five SMS attempts within five minutes. If all fail, stop retrying and continue using the working Outlook/app method where possible. This bounded test lets Microsoft try multiple delivery providers without generating prolonged repeated traffic.^2^
- Record the UTC timestamp, Request ID, Correlation ID, error code, country code +995, mobile carrier, and whether no message arrived at all.
- An administrator with at least Reports Reader access can obtain the event under Microsoft Entra admin center → Entra ID → Monitoring & health → Sign-in logs. Carrier investigations commonly require samples from the previous 48–72 hours.^3^
Determine whether this affects one number or Georgian numbers generally
- If only your number fails, ask Support to check for throttling or a phone-reputation restriction.
- If multiple users with +995 numbers fail, ask Support to verify tenant enablement for Georgian telephony and investigate regional delivery.
Georgia (+995) is on the list of regions requiring tenant opt-in for MFA telephony. That does not establish the cause here—especially because SMS previously worked—but it is an important tenant-level condition for the administrator or Support to verify.^1^
Optionally require MFA re-registration
- In Microsoft Entra admin center → Users → your account → Authentication methods, select Require re-register multifactor authentication.
- Register the phone method again during the next interactive sign-in.
This is a supported administrator-side troubleshooting action for similar 399287 cases.^4^ It is not guaranteed to remove an internal phone-reputation restriction and is not a mandatory prerequisite for opening a support case.
Open a Microsoft support case if 399287 continues
- In the Microsoft 365 admin center, select Help & support, describe the issue, and then select Contact Support.
- Request:
  “Investigate Microsoft Entra MFA SMS error 399287 for a +995 number; verify regional telephony enablement, throttling, delivery status, and any PhoneReputation/BadReputation restriction.”
- Include the fresh Correlation ID and UTC timestamp, but provide the complete phone number and tenant identifiers only through the secure support case.

Microsoft 365 business support requests normally require an administrator. If the university purchased all subscriptions through a partner, its administrator must contact that partner instead.^5^

A closely matching 399287 Q&A case was resolved after engineering cleared a backend bad-reputation restriction, confirming that such an unblock is possible when Support verifies that this is the applicable condition.^6^

Why administrator involvement cannot be avoided

The working Outlook session helps maintain access, but it does not grant permission to inspect tenant sign-in logs, verify regional telephony enablement, reset tenant-managed MFA registration, or open the organization’s Microsoft 365 support request. Public Microsoft Q&A moderators also cannot modify accounts or clear backend restrictions.^4^

Do not post the phone number, Request ID, Correlation ID, tenant ID, or screenshots containing account information publicly. Supply them privately through the university’s IT ticket and Microsoft’s secure support channel.

References