CISA.MS.EXO.4.2: The DMARC message rejection option SHALL be p=reject.
| ID | CISA.MS.EXO.4.2 |
| Severity | High |
| Suite | CISA SCuBA baselines |
| Product | Exchange Online |
| Feature | Email authentication |
| Security area | Email and collaboration protection |
| Resource type | Domain |
| User impact of fixing | Medium |
| Effort to fix | High |
| Benchmark | CISA SCuBA Secure Configuration Baselines for Microsoft 365 ScubaGear main, 2026-10-11, MS.EXO.4.2 (SHALL) |
| Framework controls | cisa-scuba:MS.EXO.4.2nist-800-53-r5:SI-8 Spam Protection |
| MITRE ATT&CK | T1566, T1598, T1684.002 |
| Reads from | Exchange Online |
What this checks and how to fix it
Section titled “What this checks and how to fix it”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:
Section titled “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
Section titled “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
Mito check, based on CISA ScubaGear. Author: soulemike; contributors: JeanPhilippeGeorge. Open-source licences.
Open-source licences. CIS Benchmark material © Center for Internet Security, Inc.; CISA SCuBA baselines are public domain (CC0).
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