Google Workspace Out Of Domain Email Forwarding — Sigma Rule

Rule metadata and linked tags

Author: Tom kluter. Source status: experimental; severity: medium. Source dates: 2026-04-28 / not supplied.

{
  "product": "gcp",
  "service": "google_workspace.login"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: e39e2f749b5650f0fdb186dc99d7da21a1abca29927496e0371529bdcfee5e88

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Google Workspace Out Of Domain Email Forwarding
id: 2a0bb2dd-eb5f-4517-8cb9-404f8ba764a5
status: experimental
description: Detects automatic email forwarding to external domains in Google Workspace, which may indicate data leakage or misuse.
references:
    - https://developers.google.com/workspace/admin/reports/v1/appendix/activity/login#email_forwarding_out_of_domain
author: Tom kluter
date: 2026-04-28
tags:
    - attack.t1114.003
    - attack.collection
logsource:
    product: gcp
    service: google_workspace.login
detection:
    selection:
        protoPayload.serviceName: 'login.googleapis.com'
        protoPayload.metadata.event.eventName: 'email_forwarding_out_of_domain'
    condition: selection
falsepositives:
    - Legitimate forwarding
level: medium

Original YAML and metadata in JSON

False positives

• Legitimate forwarding

Source references

• https://developers.google.com/workspace/admin/reports/v1/appendix/activity/login#email_forwarding_out_of_domain