🆘Phone number has bad reputation

Question

I'm an MCP working as an Independant Contractor that has multiple customers.

One of my older customers needed my help but I cannot login because it's been years since I last logged in and only have SMS/ Phone MFA and the number used apparently has been marked with a bad reputation!?

Don't know why, this is my number that I have owned for more than 30 years!

Error Code: 399287

Request Id: [Moderator note: personal information removed]

Correlation Id: [Moderator note: personal information removed]

Timestamp: 2026-02-13T12:03:53Z

Number is +45 xx xx xx xx

Please help me as I cannot log into the portal an create the case there and I cannot help the customer right now.

---

Moved from: Microsoft Security | Microsoft Identity Manager

Answer 1

Hi Liora,

Found this article from December last year:
https://learn.microsoft.com/en-us/answers/questions/5646083/phone-number-has-bad-reputation
Where a Sridevi Machavarapu help a person with the same issue, so was hoping someone else in here could do the same for me...

I guess I can try the local phone number... but normally there is no support via phone is you don't have a special support agreement...

Ps. Have YubiKeys and more that I use now a days, but like I wrote this is an old account that has not been upgraded for years.

Friendly Regards

Answer 2

Dear @Stefan B. Christensen,

Welcome to Microsoft Q&A. 

Thank you for sharing the detailed error information. Based on what you described, this behavior is expected in this specific scenario.

Error Code 399287 indicates that the SMS (or voice) MFA method has been blocked by Microsoft’s phone reputation and risk‑detection systems. When this happens, the platform will refuse to send or validate verification codes for that phone number.

This decision is made at the backend service level and is not related to the age, ownership, or long‑term validity of the phone number. Even phone numbers that have worked reliably for decades can be flagged if certain automated risk signals are detected (for example, repeated MFA retries, unusual sign‑in patterns, or tenant context changes).

This is a user‑to‑user support forum, and neither moderators nor contributors here have access to tenant backends, phone reputation systems, or MFA enforcement services. As a result, we cannot remove the “bad reputation” flag or unblock SMS MFA from here.

In cases like this, Microsoft Support/the Data Protection and Identity teams are the only teams that can review and remove the block from the backend, if appropriate.

If you’re unable to sign in to the admin portal to open a support request, you still contact Microsoft Support directly using regional support phone numbers and explain that you are blocked by Error 399287 (SMS MFA – phone reputation).

Please try to find the related hotline number to call the frontline let them raise a ticket for you: Customer service phone numbers - Microsoft Support 

Depending on your country or region, when you call the support number, you may hear an introduction of about 30 seconds such as "you can visit the link...". You can ignore this introduction and wait until you are presented with the options. Then press "1" as a business email user, and again "1" for technical help 

If you still cannot reach to agent, there is still a workaround, you might consider registering for a new tenant by signing up for a trial subscription via this link Compare All Microsoft 365 Plans | Microsoft. This would allow you to create a new tenant following the provided prompts. Once set up, you can access the admin console of the new tenant and submit a support ticket requesting to speak with the Data Protection team on behalf of your previous tenant.  

Please remember to cancel the trial subscription once your issue is resolved to avoid any unintended charges.  

When contacting support, be ready to provide:

Tenant ID

Affected user UPN

Phone number and country code

Error code 399287, along with the Request ID, Correlation ID, and Timestamp you already captured

Once the block is reviewed and cleared, Microsoft will typically recommend moving away from SMS as the primary MFA method and registering Microsoft Authenticator or another app‑based method, as SMS is more susceptible to reputation and fraud controls.

I hope this helps clarify what is happening and why you’re seeing this behavior. If my response helps you better understand the situation or points you toward the correct next step, please consider marking it as the Accepted answer, as this may also help others who encounter the same error.

Warm regards, 

---

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.