IdFix tool is an inevitable tool while deploying Microsoft Azure or Office 365 etc. What it does is, it prepare directory attributes for synchronization with Microsoft cloud services. The tool helps to find any errors on the user  objects and help to fix it before it sync it to the Microsoft cloud.

1. Once you have download the tool you can run it on the domain controller. You can follow the installation instructions as per the Microsoft documentation. Once installed launch the tool then click on the Query button to query the user objects and then it will display the errors on the screen.
2. Based on the Error displayed on the tool you can check on this page to fid the fix.

Here is a screenshot from my lab. On the bottom of the tool you will notice the number of users it queried and the number of errors it found.

3.   You don’t have to click Apply after each update. Instead, you can fix several errors before   you click Apply and IdFix will change them all at the same time. You can sort the errors by error type by clicking ERROR at the top of the column that lists the error types.

4.   One strategy is to fix all the errors of the same type; for example, fix all the duplicates first, and apply them. Next, fix the character format errors, and so on. Each time you apply the changes, the IdFix tool creates a separate log file that you can use to undo your changes in case you make a mistake. The transaction log is stored in the folder that you installed IdFix in. C:\Deployment Tools\IdFix by default.

5.   After all of your changes are made to the directory, run IdFix again to ensure that the fixes you made didn’t introduce new errors. You can repeat these steps as many times as you need to. It’s a good idea to go through the process a few times before you synchronize.

Here is video explaining the same. Do check it out.

You can download the IdFix tool from here