Suspicious Email Delivered In Microsoft 365 (via audit)

title: Suspicious Email Delivered In Microsoft 365 (via audit)
id: 42238f4a-9ffe-5e0a-aa73-476d4bace7e6
status: stable
description: This rule detects instances where an email, identified as hostile or anomalous by the Microsoft Defender for Office 365 (formerly ATP) engine, was delivered to a user's Inbox or Junk folder. It might indicate that a potential threat, such as a spearphishing attachment or links, has bypassed initial blocking mechanisms and reached an end-user, requiring further investigation and potential remediation.
references:
    - https://attack.mitre.org/techniques/T1566/002/
    - https://attack.mitre.org/techniques/T1566/001/
    - https://learn.microsoft.com/en-us/defender-office-365/threat-explorer-real-time-detections-about
    - https://research.splunk.com/cloud/605cc93a-70e4-4ee3-9a3d-1a62e8c9b6c2/
    - https://github.com/Bert-JanP/Hunting-Queries-Detection-Rules/blob/e7250648cb16d4a497ae8737943bf010ea96d2e6/Defender%20For%20Cloud%20Apps/MaliciousEmailDeliveredInMailbox.md
author: Huntrule Team
date: 2026-06-29
tags:
    - attack.initial-access
    - attack.t1566.001
    - attack.t1566.002
logsource:
    service: audit
    product: m365
detection:
    selection:
        Workload: 'ThreatIntelligence'
        Operation: 'TIMailData'
        Directionality: 'Inbound'
    filter_main_blocked:
        DeliveryAction: 'Blocked'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
level: medium