O365 Threat Intelligence Suspicious Email Delivered

name: O365 Threat Intelligence Suspicious Email Delivered
id: 605cc93a-70e4-4ee3-9a3d-1a62e8c9b6c2
version: 11
date: '2026-04-15'
author: Steven Dick
status: production
type: Anomaly
description: The following analytic identifies when a suspicious email is detected within the Microsoft Office 365 ecosystem through the Advanced Threat Protection engine and delivered to an end user. Attackers may execute several attacks through email, any detections from built-in Office 365 capabilities should be monitored and responded to appropriately. Certain premium Office 365 capabilities such as Safe Attachment and Safe Links further enhance these detection and response functions.
data_source:
    - Office 365 Universal Audit Log
search: |-
    `o365_management_activity` Workload=ThreatIntelligence Operation=TIMailData DeliveryAction!=Blocked Directionality=InBound
      | rename P2Sender as src_user, P1Sender as sender, Recipients{} as user, DeliveryAction as action
      | stats values(SenderIp) as src, values(Subject) as subject, values(user) as user, values(action) as action, values(SystemOverrides{}.Details) as reason, values(LatestDeliveryLocation) as result, values(ThreatsAndDetectionTech{}) as category, values(AttachmentData{}.FileName) as file_name, values(AttachmentData{}.FileType) as file_type, values(AttachmentData{}.SHA256) as file_hash values(DetectionMethod) as signature, min(_time) as firstTime max(_time) as lastTime, count
        BY src_user,sender,dest,vendor_account,vendor_product
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `o365_threat_intelligence_suspicious_email_delivered_filter`
how_to_implement: You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events. The threat intelligence workload is typically only visible to E3/E5 level customers.
known_false_positives: No false positives have been identified at this time.
references:
    - https://learn.microsoft.com/en-us/microsoft-365/security/office-365-security/anti-malware-protection-for-spo-odfb-teams-about?view=o365-worldwide
    - https://learn.microsoft.com/en-us/microsoft-365/security/office-365-security/office-365-ti?view=o365-worldwide
drilldown_searches:
    - name: View the detection results for - "$user$" and "$src_user$"
      search: '%original_detection_search% | search  user = "$user$" src_user = "$src_user$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user$" and "$src_user$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$", "$src_user$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: "0"
rba:
    message: A suspicious email was delivered to $user$ by $src_user$ matching the $signature$ signature
    risk_objects:
        - field: user
          type: user
          score: 20
        - field: src_user
          type: user
          score: 20
    threat_objects:
        - field: subject
          type: email_subject
tags:
    analytic_story:
        - Spearphishing Attachments
        - Suspicious Emails
    asset_type: O365 Tenant
    mitre_attack_id:
        - T1566.001
        - T1566.002
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: threat
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1566/o365_various_alerts/o365_various_alerts.log
          sourcetype: o365:management:activity
          source: o365