You can define the list of WhiteList users in the WhiteListDefinition security rule. The security rule uses the Define Symbol action to create a list of users that view unmasked data. Separate user names with a coma.
If you want to mask data based on the users in the WhiteList folder, enable the WhiteList folder and disable the BlackList folder.
For example, you want the database administrator to view unmasked data. You want everyone else to see masked data. Enable the WhiteList folder and disable the BlackList folder. List the database administrator in the WhiteListDefinition rule. Dynamic Data Masking will mask data for everyone that is not the database administrator. The database administrator will view unmasked data.