Hope you're doing well.
There can be many reasons for getting this error message. Please verify-
- If Email integration feature is enabled under Teams org-wide settings
- Make sure the sender’s email address is not blocked in the Teams Admin Center
- In advanced settings, please make sure that option that says 'allow anyone to send emails to this address' is enabled
Alternatively, you will need to contact your IT Admin. Admin can raise a support case with Microsoft Graph, a Support Engineer will be able to assist you better.
Please follow this link to raise support ticket- http://aad.portal.azure.com/ or https://admin.microsoft.com/#/support/requests.
Hope this helps.
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