The sending of online advertising is regulated by legal framework conditions. According to this, the consent of the end user is required. This consent, with which the consumer confirms his contact data and agrees to the sending of online advertising, is referred to as opt-in.
There are two variants of the opt-in: the confirmed opt-in and the double opt-in( DOI). In the case of the confirmed opt-in, an e-mail is sent to the contact data as confirmation with the specified user data in which the registration is confirmed. If the recipient does not reply, this is deemed to be consent to the opt-in.
It is different with the Double Opt-In. In this procedure, the recipient must confirm the opt-in. If the contact data provided is incorrect or if the e-mail recipient cannot be clearly identified, then he or she can correct this via the e-mail reply. With double opt-in, conversion rates are relatively low.