What is double opt-in email marketing? Double opt-in email marketing is when a subscriber has specifically asked for future communication from the list owner and confirmed that choice a second time. Simply put, double opt-in email marketing means that you only send campaigns to users who have asked to receive them and agreed to a second confirmation email. Using this type of strategy is of key importance, double opt-in email marketing is one of the single most important components of a successful campaign. Double opt-in email marketing, when done correctly, can greatly increase your open rates since you are sending your campaigns to a more receptive audience.