According to the Graph Api, emailThreatSubmission is an abstract type to report suspected spam, malware or phishing emails to Microsoft Defender for Office 365. Therefore, all user-submitted emails listed using the List emailThreatSubmissions endpoints are reported to Microsoft.
Also, it should be noted that the endpoint you are using is a /beta
version, the functionality of this version is subject to change at any time, and it is not recommended for actual production.
See this link for more information:
Hope this helps.
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