The User Exclusion list defines which rights account certificates (RACs) are not trusted by this cluster. Click Exclude RAC ...

The User Exclusion list defines which rights account certificates (RACs) are not trusted by this cluster. Click Exclude RAC to add a RAC to the exclusion list. You can exclude RACs that are assigned to internal users who have an Active Directory Domain Services account in your forest as well as RACs that are assigned to external users. Exclude a RAC that is assigned to an internal user by providing the email address of the user. Exclude a RAC that is assigned to an external user by providing the user's public key string.