Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hi Benoit Charlier,
Good day.
Thank you for reaching out to Microsoft community.
According to your description, before moving forward, could you please share with me below more information to understand your particular situation?
- Could you please share with me message header of this bounce back email via private message? Here is article to provide message header: View internet message headers in Outlook - Microsoft Support
- Furthermore, if you are global admin, could you please share with me expanded message trace result of this affected email message in private message? This article for global admin reference to run message trace: Message trace in the new EAC in Exchange Online | Microsoft Learn
Initially, I asked for some information as reconfirmation as I couldn't find more information in your topic description so that we can both understand the particular situation. If you sharing above requested information in private message, it will help us for further consultation.
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Note: To protect sensitive information, please share with me above some requested screenshot information in "View Private messages".
Here are the steps to open "View private messages":
To view private messaging options> Sign in to Microsoft Community, use the email account where you posted this thread information to Microsoft Community, > click your profile picture in the top right, > select the My Profile option.
I look forward to your next update on this in private message. In addition, I will provide you with information accordingly.
Thank you for your valuable time and kind cooperation.
Sincerely
Vaidya Darpan