UPNs are a convenient way for users to remember their usernames. A UPN essentially has the same format as an email address. Rather than having users login to their workstations or intranet resources as EXAMPLE\User, they can login as firstname.lastname@example.org which is the same as their email address. You can reduce support costs as users only have to remember one login name versus two separate ones.
When moving to Office 365, users need to login with their UPN. … Read more