Clean Your Active Directory Before Sync: IdFix Tool Complete Guide (MS-102)

Introduction

When preparing an on‑premises Active Directory for synchronization with Microsoft Entra ID (Azure AD), the most common cause of deployment failure is bad or non‑compliant directory data. Microsoft provides the IdFix Tool specifically to identify and remediate these issues before you configure Microsoft Entra Connect or Cloud Sync.

This article explains what the IdFix Tool is, why it matters, how to use it, and what MS‑102 expects you to know.

Even a small inconsistency in directory attributes can lead to:

Synchronization failures
Duplicate or missing users
Login issues in Microsoft 365
Broken email attributes

To avoid these issues, Microsoft provides a lightweight tool called IdFix.

In this guide, we’ll cover:

What IdFix is
Why it’s important
Step-by-step usage
Lab vs production scenarios
Optional hands-on testing

What is the IdFix Tool?

IdFix is a directory remediation tool that scans your Active Directory and identifies attribute issues that may block synchronization with Microsoft Entra ID.

Simple Definition

IdFix is a pre-check tool that ensures your Active Directory is ready for synchronization.

What IdFix Does (and What It Does Not)

What IdFix Does

Queries Active Directory via LDAP
Identifies attributes that will fail synchronization
Detects:
- Duplicate values
- Invalid formatting
- Unsupported characters
- Blank but required attributes
- Unverified UPN suffixes
Allows administrators to:
- Correct values
- Remove invalid data
- Export findings for offline review
- Undo changes if needed

What IdFix Does NOT Do

Automatically fix data without admin approval
Change business logic
Verify domains in Entra ID
Replace proper directory planning

IdFix is a validation and remediation tool, not a replacement for identity design.

Why IdFix is Important

Microsoft Entra ID enforces strict rules for identity attributes such as:

User Principal Name (UPN)
Email (mail)
proxyAddresses

If these attributes are incorrect:

Synchronization will fail
Users may not appear in Microsoft 365
Authentication may break

Common Issues Found

Duplicate UPNs
Invalid email formats
Missing attributes
Unsupported characters
Incorrect proxyAddresses

How IdFix Works

IdFix works in four simple steps:

Query Active Directory
Detect issues
Display results in a table
Allow fixes

Do You Need IdFix in a New Environment?

If your Active Directory is:

Newly installed
Clean with minimal users
No legacy data

You may not see any errors.

However, the best practice is:

Run IdFix once to confirm your directory is clean

Lab vs Production

Environment	IdFix Importance
Lab / New AD	Optional (validation only)
Production AD	Critical (must run)

Step 1: Download the IdFix Tool

The Microsoft Download Center link is deprecated.
Recommended: Install via MSI from GitHub
This avoids ClickOnce, proxy, TLS, and firewall issues

idfix/MSIs at master · microsoft/idfix · GitHub

Step 2: Run IdFix

Open folder
Right-click IdFix.Setup.msi
Run as Administrator
Install IdFix as per instructions

Step 3: Scan Active Directory

Click Query

Tool scans entire directory
Results displayed in a table

Understanding Columns

DN → Object location
Attribute → Problem field
Value → Current value
Error → Issue type
Update → Suggested fix

Step 4: Fix Errors

Common Error Types

Duplicate:

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Same value used by multiple objects

Fix: Ensure uniqueness

Format:

Invalid format (e.g., missing @domain.com)

Fix: Correct format

Blank:

Required attribute missing

Fix: Add value

Invalid Characters:

Unsupported symbols

Fix: Remove characters

Apply Fix:

Enter a value in the Update column
Click Apply

OR fix directly in Active Directory (recommended)

Step 5: Re-Validate

Click Query again
Ensure:
- No errors
- Clean output

Lab Demonstration (Create & Fix Issues)

If your AD is clean, you can simulate errors for learning.

Important: Do this only in lab environment

Create Sample Issues

1. Duplicate UPN

Create 2 users with the same UPN

Set-ADUser idfixuser1 -Add @{proxyAddresses="SMTP:shared@lokesh.shop"}
Set-ADUser idfixuser2 -Add @{proxyAddresses="SMTP:shared@lokesh.shop"}

2. Invalid Email

userdomain.com

Set-ADUser idfixuser1 -EmailAddress "userdomain.com"

3. Special Characters

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user#name@domain.com

Set-ADUser idfixuser2 -EmailAddress "user#name@lokesh.shop"

4. Blank Attribute

Remove the mail field

Set-ADUser idfixuser1 -Clear mail

5. Wrong Proxy Address

smtp:user@@domain.com

Set-ADUser idfixuser2 -Add @{proxyAddresses="smtp:user@@lokesh.shop"}

6. Validate before IdFix

Get-ADUser -SearchBase "OU=IdFix-Lab,DC=lokesh,DC=shop" -Filter * `
-Properties userPrincipalName,mail,proxyAddresses |
Select Name,userPrincipalName,mail,proxyAddresses