Anti-Phishing Policies in Microsoft Defender represent the front line of defense in a modern Zero Trust architecture. While traditional email filters focus on bulk “spam,” the modern threat landscape has shifted toward highly targeted identity deception, such as credential harvesting and executive impersonation.

In our previous post, we used Threat Analytics to identify active attack campaigns. Now, we move from awareness to action. Understanding how to configure Anti-Phishing Policies in Microsoft Defender is a core requirement for the MS-102 exam and a critical operational skill for any Microsoft 365 Administrator.

In this guide, we will break down the architecture of phishing protection and complete a hands-on lab to harden your tenant against spoofing and impersonation attacks.

Table of Contents

Why Anti‑Phishing Comes Next

Threat Analytics answers:

What attackers are actively doing.

Anti‑phishing policies answer:

How do I stop those attacks from reaching users?

Microsoft 365 phishing attacks commonly target:

Credentials
OAuth consent
MFA fatigue
Executive impersonation
Vendor trust

Microsoft Defender for Office 365 provides purpose‑built anti‑phishing controls that go far beyond basic spam filtering.

What is an Anti‑Phishing Policy?

Anti‑phishing policies protect users from identity‑based email attacks, including:

Domain spoofing
User impersonation
Brand impersonation
Credential harvesting
Account takeover attempts

When implementing Anti-Phishing Policies in Microsoft Defender, administrators move beyond basic content filtering to focus on sender intent and identity verification.

Unlike spam filters, anti‑phishing policies focus on who the email pretends to be, not just content or reputation.

When we look at Anti-Phishing Policies in Microsoft Defender, we aren’t just looking for bad words in an email. We are looking for identity deception. These policies are designed to protect against sophisticated social engineering that traditional spam filters often miss.

Anti‑Phishing vs Anti‑Spam (Critical Distinction)

Anti‑Spam	Anti‑Phishing
Filters bulk mail	Detects targeted deception
Reputation‑based	Identity & intent‑based
Volume attacks	Personalized attacks
Commodity threats	High‑impact threats

MS‑102 frequently tests this distinction.

Understanding the role of Anti-Phishing Policies in Microsoft Defender versus basic Anti-Spam is a major exam objective. While Anti-Spam handles the volume, Anti-Phishing handles the intent.

How Anti‑Phishing Works in Defender for Office 365

Anti‑phishing policies evaluate:

Sender identity
Header anomalies
Domain relationships
User behavior patterns
Historical trust signals

Microsoft combines machine learning with tenant context to detect high‑confidence phishing, even when links and attachments appear clean.

The intelligence behind Anti-Phishing Policies in Microsoft Defender uses machine learning to compare incoming signals against millions of known attack patterns.

Where Anti‑Phishing Policies Are Managed

Path:

Microsoft Defender portal
→ Email & collaboration
→ Policies & rules
→ Threat policies
→ Anti‑phishing

This location matters for MS‑102 scenario questions.

Key Anti‑Phishing Features

🔹 User Impersonation Protection

Detects emails pretending to be:

Executives
High‑value employees

🔹 Domain Impersonation Protection

Detects look‑alike domains attempting brand abuse.

🔹 Spoof Intelligence

Identifies and blocks false sender domains.

🔹 Phishing Thresholds

Controls detection sensitivity.

MS‑102 Exam Insight

MS‑102 emphasizes:

When to use anti‑phishing vs spam
How impersonation protection works
Policy scope and precedence
Admin action when phishing is detected

Hands‑On Lab: Configure Anti‑Phishing Protection

This lab will walk you through the manual configuration of Anti-Phishing Policies in Microsoft Defender to protect high-value users from impersonation.

Lab Objective
Review and configure an anti‑phishing policy to protect users against impersonation and spoofing attacks.

Lab Prerequisites

Microsoft Defender for Office 365 (Plan 1 or Plan 2)
Security Administrator or Global Administrator role
Test tenant (recommended)

Step 1: Open Anti‑Phishing Policies

Go to the Microsoft Defender portal
Navigate to: Email & collaboration → Policies & rules → Threat policies → Anti‑phishing
Review the Default anti‑phishing policy

Note that Microsoft enables baseline protection by default.

Step 2: Review Default Policy Settings

Examine:

Impersonation protection status
Protected users
Spoof intelligence
Action settings

Understand what is already active before creating custom policies.

Step 3: Create a Custom Anti‑Phishing Policy

Select Create

Name the policy: Anti‑Phishing – Protected Users
Proceed through policy setup

Step 4: Assign Policy Scope

Apply the policy to:

A test group
Or selected users

Avoid tenant‑wide rollout in first iteration.

Step 5: Configure Protection Settings (Spoof Intelligence)

In this step, spoof‑based protections are reviewed and enabled to help protect users against domain spoofing and sender impersonation attempts.

Configuration

Under Protection settings, ensure the following options are configured:

Spoof intelligence: On
Honor DMARC record policy when spoof is detected: On
Unauthenticated senders symbol (?) for spoof: On
Show “via” tag: On

These settings enable Microsoft Defender for Office 365 to:

Detect spoofed sender domains
Apply DMARC enforcement (quarantine or reject)
Visually warn users about unverified senders

Actions Configuration

Verify that actions are set appropriately:

If spoof is detected and DMARC policy = p=quarantine
→ Quarantine the message
If spoof is detected and DMARC policy = p=reject
→ Reject the message
If spoof is detected by spoof intelligence
→ Move to Junk Email folder

These actions provide layered protection while reducing the risk of false positives.

Step 6: Configure Actions

Set actions such as:

Move the message to quarantine
Enable safety tips
Alert administrators

Avoid delete actions initially in production environments.

Step 7: Review Policy Precedence

Confirm:

Interaction with the default policy

Higher priority policies override lower priority ones.

Lab Note:
User and domain impersonation protection are available only with Microsoft Defender for Office 365 Plan 2. This lab tenant uses Defender for Office 365 Plan 1, so impersonation protection options are not available in the anti-phishing policy configuration. For MS-102, administrators are expected to understand where impersonation protection is configured and that it is license-dependent, not to configure it in every lab environment.

In tenants licensed with Microsoft Defender for Office 365 Plan 2, anti‑phishing policies also support user and domain impersonation protection, allowing administrators to protect executives and high‑value users against targeted identity‑based attacks.

Senior Engineer Tip: "On the MS-102, if a question mentions 'User Impersonation' or 'Executive Protection,' you must immediately think Defender for Office 365 Plan 2. This is one of the most common 'licensing' traps on the exam. If the lab environment only has Plan 1, focus your mastery on Spoof Intelligence, which is the core protection available at both levels."

Common Anti‑Phishing Mistakes

A common error is assuming that the default Anti-Phishing Policies in Microsoft Defender are enough; for executive protection, custom policies are almost always required