user principal name suffix (n)~ The part of the user principal name (UPN) to the right of the @ character. The default UPN suffix for a user account is the DNS domain name of the domain that contains the user account. Alternative UPN suffixes may be added to simplify administration and user logon processes by providing a single UPN suffix for all users. The UPN suffix is only used within the Active Directory forest and it is not required to be a valid DNS domain name.