Hello Tom,
My name is EngineTyme, an Independent Advisor and a Microsoft user like you and I would be glad to help you.
To enable reporting of external messages in Teams, you need to ensure that the user reporting settings are enabled for Teams messages in the Teams admin center and the Microsoft Defender portal.
Here are the steps to enable user reporting settings for Teams messages in the Teams admin center:
1. Go to the Teams admin center at https://admin.teams.microsoft.com.
2. Navigate to the Messaging policies page.
3. Select the Manage policies tab and edit the appropriate policy (the Global (Org-wide) default policy or a custom policy).
4. In the policy details page that opens, find the Report a security concern toggle and turn it on.
5. Select Save, and then select Confirm in the confirmation dialog that opens.
If user reporting of messages is turned on in the Teams admin center, it also needs to be turned on in the Defender portal for user reported messages to show up correctly on the User reported tab on the Submissions page.
To turn on user reporting of messages in the Defender portal, follow these steps:
1. Go to the Microsoft Defender portal at https://security.microsoft.com/securitysettings/userSubmission.
2. Go to the Microsoft Teams section for the Monitor reported messages in Microsoft Teams setting.
3. Turn on the Monitor reported messages in Microsoft Teams setting.
Please note that user reporting of messages in Teams is not supported in U.S. Government organizations (Microsoft 365 GCC, GCC High, and DoD)
User reported message settings in Microsoft Teams: https://learn.microsoft.com/microsoft-365/security/office-365-security/submissions-teams?view=o365-worldwide
Report messages in Microsoft Teams: https://support.microsoft.com/office/c7a69a60-767b-4288-8713-7c28b4a73913
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Please let me know if you have any questions or concern.
Best regards,
EngineTyme.