CISA.MS.EXO.4.2 - The DMARC message rejection option SHALL be p=reject.
Overview
The DMARC message rejection option SHALL be p=reject.
Rationale: Of the three policy options (i.e., none, quarantine, and reject), reject provides the strongest protection. Reject is the level of protection required by BOD 18-01 for FCEB departments and agencies.
Remediation action:
- See MS.EXO.4.1v1 Instructions for an overview of how to publish and check a DMARC record.
- Ensure the record published includes p=reject.
Related links
- Exchange admin center - Accepted domains
- CISA 4 Domain-Based Message Authentication, Reporting, and Conformance (DMARC) - MS.EXO.4.2v1
- CISA ScubaGear Rego Reference
Test Metadata
| Field | Value |
|---|---|
| Test ID | CISA.MS.EXO.4.2 |
| Severity | High |
| Suite | CISA |
| Product | Exchange Online |
| Feature | Email authentication |
| Area | Email and collaboration protection |
| Resource type | Domain |
| User impact | Medium |
| Implementation cost | High |
| MITRE ATT&CK | T1566 Phishing, T1598 Phishing for Information, T1684.002 Email Spoofing |
| Supports benchmark | CISA SCuBA Secure Configuration Baselines for Microsoft 365 (version ScubaGear main, 2026-10-11), requirement MS.EXO.4.2 |
| Criticality | SHALL |
| Upstream requirement | MS.EXO.4.2v1 |
| Supports controls | cisa-scuba:MS.EXO.4.2, nist-800-53-r5:SI-8 |
| PowerShell test | Test-MtCisaDmarcRecordReject |
| Services | ExchangeOnline |
Source
- Test:
tests/cisa/exchange/Test.CISA.MS.EXO.4.2.ps1 - Documentation:
tests/cisa/exchange/Test.CISA.MS.EXO.4.2.md