Opt-In eyepin Support Updated April 16, 2019 14:44 Follow Subscriber gives permission to the email sender to contact him. In terms of email marketing, three different registration methods have established: Single Opt-In, Confirmed Opt-In and Double Opt-In. Related articles Single Opt-In Double Opt-In How do I create a Newsletter registration form? What Opt-Out Settings are there? What is Email Marketing? Comments 0 comments Please sign in to leave a comment.