Script Download: The script is available for download from https://gallery.technet.microsoft.com//How-to-Remove-Un-existed-5d36c14d. You can also use Microsoft Script Browser for Windows PowerShell ISE to download the sample with one button click from within your scripting environment.
This script will remove Un-existed User from Public Folder permission list in Exchange.
You can find more All-In-One Script Framework script samples at http://aka.ms/onescriptingallery