The single-opt-in procedure describes the ordering or registration of a user, for example for the distribution list of a newsletter, without confirming it again.


The user completes an online form and is automatically included in the respective mailing list after sending the form once. If the user cancels the subscription, it will be deleted from the mailing list immediately, without further request. This is referred to as single-opt-out.


In contrast to the double-opt-in procedure, the advertiser risks invalid applications due to the lack of additional consent.