Information
You should review the Malware Detections report at least weekly. This report shows specific instances of Microsoft blocking a malware attachment from reaching your users.
Rationale:
While this report isn't strictly actionable, reviewing it will give you a sense of the overall volume of malware being targeted at your users, which may prompt you to adopt more aggressive malware mitigations.
NOTE: Nessus has not performed this check. Please review the benchmark to ensure target compliance.
Solution
To review the report, use the Microsoft 365 Admin Center:
Select Security (also at https://protection.office.com).
Expand Reports then select Dashboard.
Review the Malware Detected in Email report.