Detection rules › Sigma
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 coverage
| Tactic | Techniques |
|---|---|
| Initial Access | T1566.001 Phishing: Spearphishing Attachment, T1566.002 Phishing: Spearphishing Link |
Event coverage
| Provider | Event |
|---|---|
| M365-ThreatIntelligence | TIMailData |
Rules detecting the same action
Other rules on this platform that filter on the same API call or operation.
Rule body yaml
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
Stages and Predicates
Stage 0: condition
selection and not 1 of filter_main_*Stage 1: selection
selection:
Workload: 'ThreatIntelligence'
Operation: 'TIMailData'
Directionality: 'Inbound'
Stage 2: not filter_main_blocked
filter_main_blocked:
DeliveryAction: 'Blocked'
Exclusions
Top-level NOT(...) conjuncts: predicates this rule actively suppresses.
| Field | Kind | Excluded values |
|---|---|---|
DeliveryAction | eq | Blocked |
Indicators
Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.
| Field | Kind | Values |
|---|---|---|
Directionality | eq |
|
Operation | eq |
|
Workload | eq |
|