Allowed domains SHALL NOT be added to inbound anti-spam protection policies

Contributed by Michael Soule with Thomas SchmidtAll contributors →

Part of CISA · Exchange Online · Anti-spam · All checks

Run this check

Invoke-Maester -TestId CISA.MS.EXO.14.3

Overview

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

1. Sign in to Microsoft 365 Defender.
2. In the left-hand menu, go to Email & Collaboration > Policies & Rules.
3. Select Threat Policies.
4. From the Templated policies section, select Preset Security Policies.
5. Under Standard protection, slide the toggle switch to the right so the text next to the toggle reads Standard protection is on.
6. 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

• Defender admin center - Preset security policies
• CISA 14 Inbound Anti-Spam Protections - MS.EXO.14.3
• CISA ScubaGear Rego Reference

Details

Every attribute of this check

Field	Value
Test ID	CISA.MS.EXO.14.3
Severity	Medium
Suite	CISA
Product	Exchange Online
Related products	Defender
Feature	Anti-spam
Area	Email and collaboration protection
Resource type	Policy
User impact	Low
Implementation cost	Medium
MITRE ATT&CK	T1566 Phishing, T1684.002 Email Spoofing
Supports benchmark	CISA SCuBA Secure Configuration Baselines for Microsoft 365 (version ScubaGear main, 2026-10-11), requirement MS.EXO.14.3
Criticality	SHALL
Upstream requirement	Moved to MS.SECURITYSUITE.6.2v1 (was MS.EXO.14.3v2)
Supports controls	cisa-scuba:MS.EXO.14.3, nist-800-53-r5:SI-8
PowerShell test	Test-MtCisaSpamBypass
Services	ExchangeOnline

Source

• Test: tests/cisa/exchange/Test.CISA.MS.EXO.14.3.ps1
• Documentation: tests/cisa/exchange/Test.CISA.MS.EXO.14.3.md