As a rule, the product do not allow tagging users to comments that do not have access to (i.e. the users should be able to access the campaign, the idea and/or the comment itself.
In case there is an attempt to do so, the tagging user will be notified with the below error message.
To allow users access to the campaign, the sysadmin/campaign manager can add them to the campaign audience through the Campaign Management menu. Click here to learn how.
Extending access to the idea to specific roles, can be managed via the self admin settings as explained here.
Moderator comments can only be accessed by the campaign managers, sysadmin, subsystem admins and tenant admins.
For more information on how to configure User Tagging Notification, please visit this article.