I am not sure what your question is exactly because as far as I know without supplemental software certificates are not sent to anyone. Are you referring perhaps to uncanny certificate in an email plugin functionality? If your goal is stopping viewers from seeing their certificates when they click on a certificate link either at the back end or on the front end without perhaps paying a fee for their certificate or for identity verification in a popup required by government agencies, then you can do that with a certificate interceptor snippet. I wrote such a thing for LearnDash 11 years ago in order to fulfill spec requirements for the state of California in their Certified Nursing Program.