# SMTP AUTH SHALL be disabled

SMTP AUTH SHALL be disabled. A Maester check for Exchange Online, Client access.

Source: https://maester.dev/docs/tests/CISA.MS.EXO.5.1

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<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/merill" title="Merill Fernando · Co-contributor"><img src="https://github.com/merill.png" alt="Merill Fernando" 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/merill">Merill Fernando</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 · Client access · <a href="/docs/tests">All checks</a></p>

```powershell title="Run this check"
Invoke-Maester -TestId CISA.MS.EXO.5.1
```

## Overview

SMTP AUTH SHALL be disabled.

Rationale: SMTP AUTH is not used or needed by modern email clients. Therefore, disabling it as the global default conforms to the principle of least functionality.

#### Remediation action:

1. To disable SMTP AUTH for the organization:
2. Sign in to the **Exchange admin center**.
3. On the left hand pane, select [**Settings**](https://admin.exchange.microsoft.com/#/settings); then from the settings list, select **Mail Flow**.
4. Make sure the setting **Turn off SMTP AUTH protocol for your organization** is checked.

#### Related links

* [Exchange admin center - Settings](https://admin.exchange.microsoft.com/#/settings)
* [CISA 5 Simple Mail Transfer Protocol Authentication - MS.EXO.5.1v1](https://github.com/cisagov/ScubaGear/blob/main/PowerShell/ScubaGear/baselines/exo.md#msexo51v1)
* [CISA ScubaGear Rego Reference](https://github.com/cisagov/ScubaGear/blob/main/PowerShell/ScubaGear/Rego/EXOConfig.rego#L306)

## Details

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

| Field | Value |
| --- | --- |
| Test ID | CISA.MS.EXO.5.1 |
| Severity | High |
| Suite | CISA |
| Product | Exchange Online |
| Feature | Client access |
| Area | Authentication |
| Resource type | Tenant |
| User impact | Medium |
| Implementation cost | Medium |
| MITRE ATT&CK | None |
| Supports benchmark | CISA SCuBA Secure Configuration Baselines for Microsoft 365 (version ScubaGear main, 2026-10-11), requirement MS.EXO.5.1 |
| Criticality | SHALL |
| Upstream requirement | MS.EXO.5.1v1 |
| Supports controls | cisa-scuba:MS.EXO.5.1, nist-800-53-r5:CM-7 |
| PowerShell test | [Test-MtCisaSmtpAuthentication](https://github.com/maester365/maester/blob/main/tests/cisa/exchange/Test.CISA.MS.EXO.5.1.ps1) |
| Services | ExchangeOnline |

</details>

## Source

- Test: [`tests/cisa/exchange/Test.CISA.MS.EXO.5.1.ps1`](https://github.com/maester365/maester/blob/main/tests/cisa/exchange/Test.CISA.MS.EXO.5.1.ps1)
- Documentation: [`tests/cisa/exchange/Test.CISA.MS.EXO.5.1.md`](https://github.com/maester365/maester/blob/main/tests/cisa/exchange/Test.CISA.MS.EXO.5.1.md)