Impersonation protection allows you mark 350 VIP users to have them additionally protected from attacks who try to impersonate them. You can add them individually to your policies.  But it contains a painful process of having to individually click all the users you want to add...

Requirement

Installation of the exchange online powershell module:

https://learn.microsoft.com/en-us/powershell/exchange/exchange-online-powershell-v2?view=exchange-ps#install-and-maintain-the-exchange-online-powershell-module

This script will allow you to import a CSV that contains all of your users that you want to protect from impersonation. A sample CSV is provided so you know how to format it.