This is one of the core EPRIVO technologies. As a sender, your emails are controlled by rules you set per each email you send. A sender retains control over privacy even for sent emails. For example, you as a sender can expire an email anytime (some subscription types) and emails will expire at the set times in the recipients’ devices. Since each email requires authentication and authorization with EPRIVO cloud service to be viewed, this cannot be circumvented. Please see a blog about additional sender-controlled features here.