Microsoft 365 – Outbound emails rejected by Outlook.com with error 550 5.7.1 (AS9031519)

I notice that you are using English in a French-language forum, so I will respond to you in English. Should you have any other preferences during our discussion, please do not hesitate to inform me. Thank you for your understanding.

Dear @SLIM FARES ,

Based on the information available to me, there is currently an ongoing Exchange service issue messages to Outlook.com, Hotmail.com, or Live.com addresses. Affected users may receive Non-Delivery Reports (NDRs) citing 550 5.7.1 or 550 5.7.23 errors related to SPF validation failures. This advisory is currently active and classified as a service degradation.

Microsoft is actively investigating the underlying cause of this email delivery issue, and engineering teams are actively analyzing service telemetry and customer-provided data to identify the source of the issue. 

I sincerely apologize for the inconvenience this ongoing issue may be causing. I understand how critical reliable email delivery is to your business operations, and I appreciate your patience while Microsoft works to identify the root cause and restore normal service as quickly as possible.

If you continue to experience this issue, please contact Microsoft Support Team and provide fresh Network Message IDs, relevant message logs, and examples of affected messages in .eml format so that they can be included in the investigation.

For business support:   

1. Find your Microsoft 365 admin: If you're not an admin and don't know who the admin is in your organization, you can find guidance here: How can I find my Microsoft 365 admin? - Microsoft Support    
2. Submit a service request: The Global Administrator should create a support request with Microsoft to receive advanced technical assistance. For detailed instructions, see: Get support - Microsoft 365 admin | Microsoft Learn    

Note: If your subscription is from a partner or reseller, contact the reseller's support provider to help open a service request on behalf of you instead.    

Thank you again for your understanding. I’ll provide additional updates as soon as more information becomes available.