CISA.MS.EXO.14.3: Allowed domains SHALL NOT be added to inbound anti-spam protection policies.
| ID | CISA.MS.EXO.14.3 |
| Severity | Medium |
| Suite | CISA SCuBA baselines |
| Product | Exchange Online |
| Related products | Defender |
| Feature | Anti-spam |
| Security area | Email and collaboration protection |
| Resource type | Policy |
| User impact of fixing | Low |
| Effort to fix | Medium |
| Benchmark | CISA SCuBA Secure Configuration Baselines for Microsoft 365 ScubaGear main, 2026-10-11, MS.EXO.14.3 (SHALL) |
| Framework controls | cisa-scuba:MS.EXO.14.3nist-800-53-r5:SI-8 Spam Protection |
| MITRE ATT&CK | T1566, T1684.002 |
| Reads from | Exchange Online, Security & Compliance PowerShell |
What this checks and how to fix it
Section titled “What this checks and how to fix it”Allowed domains SHALL NOT be added to inbound anti-spam protection policies.
Rationale: Legitimate emails may be incorrectly filtered by spam protections. Adding allowed senders is an acceptable method of combating these false positives. Allowing an entire domain, especially a common domain like office.com, however, provides for a large number of potentially unknown users to bypass spam protections.
Remediation action
Section titled “Remediation action”- Sign in to Microsoft 365 Defender.
- In the left-hand menu, go to Email & Collaboration > Policies & Rules.
- Select Threat Policies.
- From the Templated policies section, select Preset Security Policies.
- Under Standard protection, slide the toggle switch to the right so the text next to the toggle reads Standard protection is on.
- Under Strict protection, slide the toggle switch to the right so the text next to the toggle reads Strict protection is on.
Note: If the toggle slider in step 5 is grayed out, click on Manage protection settings instead and configure the policy settings according to Use the Microsoft 365 Defender portal to assign Standard and Strict preset security policies to users | Microsoft Learn.
Related links
Section titled “Related links”- Defender admin center - Preset security policies
- CISA 14 Inbound Anti-Spam Protections - MS.EXO.14.3
- CISA ScubaGear Rego Reference
Mito check, based on CISA ScubaGear. Author: soulemike; contributors: thomas-s-schmidt. 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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