Your own domains are not being allow listed in an unsafe manner in Anti-Spam Policies

Contributed by Thomas SchmidtAll contributors →

Part of ORCA · Defender · Anti-spam · All checks

Run this check

Invoke-Maester -TestId ORCA.118.3

Overview

Emails coming from allow listed domains bypass several layers of protection within Exchange Online Protection. When allow listing your own domains, an attacker can spoof any account in your organisation that has this domain. This is a significant phishing attack vector.

Remediation action

Remove allow listing on domains belonging to your organisation.

Related Links

• Microsoft 365 Defender Portal - Anti-spam settings
• Use Anti-Spam Policy Sender/Domain Allow lists

Details

Every attribute of this check

Field	Value
Test ID	ORCA.118.3
Severity	High
Suite	ORCA
Product	Defender
Related products	Exchange Online
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 controls	nist-800-53-r5:SI-8
PowerShell test	Test-ORCA118_3
Services	ExchangeOnline

Source

• Test: tests/orca/Test.ORCA.118.3.ps1
• Documentation: tests/orca/Test.ORCA.118.3.md