New Tenant MFA Error 399287 – SMS error

Question

Hello,

I have just set up a new Microsoft 365 tenant, but I am completely unable to log in via MFA using SMS (only with MS auth app). Tried to create new users, re-register mfa etc, but with no luck. Problems with all users and all numbers

We need to user sms as secondary/bakcup login.

Technical Details for Engineering:

Error Code: 399287

[Moderator note: Personal information removed]

Timestamp: 2026-02-17T07:09:49Z

I would appreciate a prompt resolution to this problem. Please let me know what information is necessary from my side to proceed.

Answer 1

Hello Arturas Babickas,

Thank you for sharing your details with us over Private Message.

I have reached out to the engineering team to unblock MFA for your account. They have now unblocked it from the backend and removed the bad reputation on it. You should be able to log in to the Azure Portal without any issues.

Please try logging in and check if you can complete SMS authentication without any errors. Let me know if you encounter any issues.

As a best practice, I recommend registering the Microsoft Authenticator method for your account instead of relying on SMS. SMS and voice call authentication methods are more vulnerable to IRSF attacks (telephony fraud) and are generally less secure.

I hope this information is helpful. Please feel free to reach out if you have any further questions.

If this answers your query, do click and Yes for was this answer helpful, which may help members with similar questions. If you have any other questions, let me know in the “comments” and I would be happy to help you.