sigmamediumHunting

Suspicious Email Delivered In Microsoft 365

Detects instances where an email, identified as malicious or suspicious 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.

MITRE ATT&CK

T1566.001 T1566.002

initial-access

Detection Query

selection:
  Workload: ThreatIntelligence
  Operation: TIMailData
  Directionality: Inbound
filter_main_blocked:
  DeliveryAction: Blocked
condition: selection and not 1 of filter_main_*

Author

Marco Pedrinazzi (@pedrinazziM) (InTheCyber)

Created

2026-01-27

Data Sources

m365audit

Platforms

m365

References

Tags

attack.initial-accessattack.t1566.001attack.t1566.002

Raw Content

title: Suspicious Email Delivered In Microsoft 365
id: 3569aefd-e535-4391-8c18-24bd01a21eaf
status: experimental
description: |
    Detects instances where an email, identified as malicious or suspicious 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://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: Marco Pedrinazzi (@pedrinazziM) (InTheCyber)
date: 2026-01-27
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:
    - Unlikely
level: medium