# The DMARC message rejection option SHALL be p=reject

The DMARC message rejection option SHALL be p=reject. A Maester check for Exchange Online, Email authentication.

Source: https://maester.dev/docs/tests/CISA.MS.EXO.4.2

<!-- This file is generated by website/scripts/generate-test-docs.mjs. Do not edit manually. -->

<div class="test-byline"><div class="test-byline-avatars"><a class="test-byline-avatar test-byline-avatar--author" href="/contributors/soulemike" title="Michael Soule · Original author"><img src="https://github.com/soulemike.png" alt="Michael Soule" width="28" height="28" loading="lazy" decoding="async" /></a><a class="test-byline-avatar" href="/contributors/jeanphilippegeorge" title="Jean-Philippe George · Co-contributor"><img src="https://github.com/JeanPhilippeGeorge.png" alt="Jean-Philippe George" width="28" height="28" loading="lazy" decoding="async" /></a></div><div class="test-byline-meta"><span class="test-byline-text">Contributed by <a href="/contributors/soulemike">Michael Soule</a> with <a href="/contributors/jeanphilippegeorge">Jean-Philippe George</a></span><a class="test-byline-link" href="/contributors">All contributors →</a></div></div>

<p class="test-part">Part of <a href="/docs/tests/cisa">CISA</a> · Exchange Online · Email authentication · <a href="/docs/tests">All checks</a></p>

```powershell title="Run this check"
Invoke-Maester -TestId CISA.MS.EXO.4.2
```

## 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](https://admin.exchange.microsoft.com/#/accepteddomains)
* [CISA 4 Domain-Based Message Authentication, Reporting, and Conformance (DMARC) - MS.EXO.4.2v1](https://github.com/cisagov/ScubaGear/blob/main/PowerShell/ScubaGear/baselines/exo.md#msexo42v1)
* [CISA ScubaGear Rego Reference](https://github.com/cisagov/ScubaGear/blob/main/PowerShell/ScubaGear/Rego/EXOConfig.rego#L176)

## Details

<details>
<summary>Every attribute of this check</summary>

| 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](https://github.com/maester365/maester/blob/main/tests/cisa/exchange/Test.CISA.MS.EXO.4.2.ps1) |
| Services | ExchangeOnline |

</details>

## Source

- Test: [`tests/cisa/exchange/Test.CISA.MS.EXO.4.2.ps1`](https://github.com/maester365/maester/blob/main/tests/cisa/exchange/Test.CISA.MS.EXO.4.2.ps1)
- Documentation: [`tests/cisa/exchange/Test.CISA.MS.EXO.4.2.md`](https://github.com/maester365/maester/blob/main/tests/cisa/exchange/Test.CISA.MS.EXO.4.2.md)