A pop-up message appears when a sharing rule is saved after selecting the Portal Roles, Portal Roles and Subordinates, or Roles, Internal and Portal Subordinates sharing rule category
How: From Setup, in the Quick Find box, enter Sharing Settings, then select Sharing Settings. Create a sharing rule and specify the users who get access to the data. For Share with, select the Portal Roles, Portal Roles and Subordinates, and Roles, Internal and Portal Subordinates sharing rule category. After you click Save, a pop-up message informs you that your data will be shared to external users. To continue, click OK