"AD Tidy is a completely free tool that I created to help other IT Pros out. It can be used to identify when user/computer accounts last logged on to the network and can tidy up these accounts in various different ways."
Adding a User Principal Name, or UPN, to Active Directory lets you match user logon names to email addresses, for example, among other things. This page describes how to add a UPN to Active Directory, so you can assign the alternate name to a user in Active Directory Users and Computers.