A double opt-in is adds an additional step to the email subscription opt-in process, requiring a user to verify their email address and confirm their consent to receive emails.

Double opt-ins signify a higher level of user interest, though its effectiveness has been both lauded and disputed by marketers.

Double opt-ins result in a higher quality final audience (the profiles that receive emails) but on the other hand users are required to perform another Action – they could for example overlook the confirmation request email, resulting in shortened email lists.