Some marketers call closed-loop opt-in "double opt-in". This term was coined by marketers in the late 90s to differentiate it from what they call "single opt-in", where a new subscriber to an email list gets a confirmation email telling them they will begin to receive emails if they take no action. Some marketers contend that "double opt-in" is like asking for permission twice and that it constitutes unnecessary interference with someone who has already said they want to hear from the marketer. However, it does drastically reduce the likelihood of someone being signed up to an email list by another person.