M365EXO-016: DKIM enabled for all domains (MS.EXO.3.1)
- Platform
- Entra ID / M365
- Category
- Advanced Threat Protection
- Severity
- High
- Zero Trust pillar
- Applications & Workloads (weight 2)
- Golden fixtures
- 3
- Branch coverage
- Observed: fixtures prove the verdicts they exercise
- Provenance
- baseline
What it checks
SCuBA MS.EXO.3.1 recommends that DKIM be enabled for all domains. DKIM adds a cryptographic signature to the message header so recipients can verify message integrity and authenticity. Without DKIM, recipients have one fewer signal to detect spoofed mail and DMARC alignment cannot rely on DKIM, weakening overall email authentication.
Recommended value
DKIM signing enabled for every custom domain with the corresponding selector CNAME records published in DNS
Remediation
Enable DKIM signing in Exchange Online for every custom domain and publish the two selector CNAME records that the service generates in the domain's DNS. Verify that the signing configuration reports an Enabled state once the CNAME records propagate. Rotate keys periodically and confirm that newly added domains have DKIM enabled as part of domain onboarding.
Fixture-proven verdicts
Every verdict below is proven by a golden fixture in the module's gating test suite. This table derives from the last green run; it cannot be edited by hand.
| Scenario | Expected verdict |
|---|---|
| clean | PASS |
| known-bad | FAIL |
| throttled | Not Assessed |
Framework mappings
- CISA SCuBA
- MS.EXO.3.1v1
- NIST SP 800-53
- SI-8
- MITRE ATT&CK
- T1566.001
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Guerrilla is written and maintained by Jim Tyler. This copy lives on jimtyler.org; the project also publishes at guerrilla.army.