MessageDesk provides users with the ability to add custom fields to contacts. You can then create filter groups based on which contacts have the same custom field values.
For example, you could create a custom field called "Customer or Staff". Then you can set this field to "staff" for any contacts who are staff members or "Customers" for any contact who is a customer.
From here you can create a filter group that contains all "Staff" members and another filter group for "Customers".
If you want to learn how you can make your own custom filter group follow the steps below.
Update custom field value for all your contacts with a csv upload (learn how here)
Create a filter group based on the custom field