Prevent Send As and Send on Behalf Of Task emails from Action in Workflow

We have Task emails that are sent to recipient fee earners in our environment to Approve or Decline over email, as opposed to clicking into the Workflow To Do list to action the item. It has come to light that delegates of the fee earners who have "Send As" or "Send on Behalf Of" associated access in Outlook Exchange, are able to reply to K2 as the fee earners or on behalf of the fee earners, and K2 will process the action. Alternatively, is it possible to set up all Task Emails that are issued from K2 for action, as "Private" so they will only be delivered and be visible to the recipient of the task, and delegates will not be able to see these.

https://community.nintex.com/archive-25/cash-management-approve-on-behalf-of-action-4111