splunk_escuTTP

O365 Email Suspicious Behavior Alert

The following analytic identifies when one of O365 the built-in security detections for suspicious email behaviors are triggered. These alerts often indicate that an attacker may have compromised a mailbox within the environment. Any detections from built-in Office 365 capabilities should be monitored and responded to appropriately. Certain premium Office 365 capabilities further enhance these detection and response functions.

MITRE ATT&CK

T1114.003

Detection Query

`o365_management_activity` Workload=SecurityComplianceCenter Operation=AlertEntityGenerated Name IN ("Suspicious email sending patterns detected","User restricted from sending email","Suspicious Email Forwarding Activity","Email sending limit exceeded")
  | fromjson Data
  | rename Name as signature, AlertId as signature_id, ObjectId as user
  | fillnull
  | stats count min(_time) as firstTime max(_time) as lastTime
    BY dest user src
       vendor_account vendor_product signature
       signature_id
  | `security_content_ctime(firstTime)`
  | `security_content_ctime(lastTime)`
  | `o365_email_suspicious_behavior_alert_filter`

Author

Steven Dick

Created

2026-03-10

Data Sources

Office 365 Universal Audit Log

References

https://learn.microsoft.com/en-us/purview/alert-policies

Tags

Suspicious EmailsOffice 365 Collection TechniquesOffice 365 Account Takeover

Raw Content

name: O365 Email Suspicious Behavior Alert
id: 85c7555a-05af-4322-81aa-76b4ddf52baa
version: 9
date: '2026-03-10'
author: Steven Dick
status: production
type: TTP
description: The following analytic identifies when one of O365 the built-in security detections for suspicious email behaviors are triggered.  These alerts often indicate that an attacker may have compromised a mailbox within the environment. Any detections from built-in Office 365 capabilities should be monitored and responded to appropriately. Certain premium Office 365 capabilities further enhance these detection and response functions.
data_source:
    - Office 365 Universal Audit Log
search: |-
    `o365_management_activity` Workload=SecurityComplianceCenter Operation=AlertEntityGenerated Name IN ("Suspicious email sending patterns detected","User restricted from sending email","Suspicious Email Forwarding Activity","Email sending limit exceeded")
      | fromjson Data
      | rename Name as signature, AlertId as signature_id, ObjectId as user
      | fillnull
      | stats count min(_time) as firstTime max(_time) as lastTime
        BY dest user src
           vendor_account vendor_product signature
           signature_id
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `o365_email_suspicious_behavior_alert_filter`
how_to_implement: You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events. The alerts must be enabled in the o365 security portal.
known_false_positives: Users emailing for legitimate business purposes that appear suspicious.
references:
    - https://learn.microsoft.com/en-us/purview/alert-policies
drilldown_searches:
    - name: View the detection results for - "$user$"
      search: '%original_detection_search% | search  user = "$user$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$") starthoursago=168  | 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: $info_min_time$
      latest_offset: $info_max_time$
rba:
    message: The user $user$ triggered the O365 security alert [$signature$]
    risk_objects:
        - field: user
          type: user
          score: 50
    threat_objects: []
tags:
    analytic_story:
        - Suspicious Emails
        - Office 365 Collection Techniques
        - Office 365 Account Takeover
    asset_type: O365 Tenant
    mitre_attack_id:
        - T1114.003
    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