M365EXO-006: DKIM/DMARC/SPF validation
- Platform
- Entra ID / M365
- Category
- Advanced Threat Protection
- Severity
- Critical
- Zero Trust pillar
- Applications & Workloads (weight 2)
- Golden fixtures
- 2
- Branch coverage
- Observed: fixtures prove the verdicts they exercise
- Provenance
- baseline
What it checks
DKIM, DMARC, and SPF are email authentication protocols that verify sender identity and prevent domain spoofing. Without all three protocols properly configured, attackers can send emails that appear to originate from your organization's domain, enabling highly convincing phishing campaigns against employees, customers, and partners. Complete email authentication is a fundamental defense against business email compromise and domain impersonation.
Recommended value
SPF record with -all (hard fail); DKIM signing enabled for all domains; DMARC policy set to reject or quarantine with aggregate reporting enabled
Remediation
Verify that each organizational domain has a valid SPF record ending with -all (hard fail) that includes all authorized sending sources. Enable DKIM signing in Exchange Online for all custom domains and publish the DKIM CNAME records in DNS. Publish a DMARC record for each domain starting with a policy of none for monitoring, then progressively move to quarantine and finally reject once legitimate sending sources are confirmed, with aggregate reports configured for ongoing visibility.
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 |
| throttled | Not Assessed |
Framework mappings
- CISA SCuBA
- MS.EXO.2.2v3, MS.EXO.3.1v1, MS.EXO.4.1v1, MS.EXO.4.2v1
- NIST SP 800-53
- SI-8
- CIS M365 Benchmark
- 2.1.9
- MITRE ATT&CK
- T1566.001