Double opt-in is a process in email marketing in which a person confirms their email address twice to ensure that they are actually interested in receiving emails from a particular sender.

The procedure usually works as follows: When a person signs up for a newsletter or other email communication, a confirmation email is sent to the email address provided. In this email, the person is asked to confirm their registration by clicking on a confirmation link or giving their consent in some other way.

Only when the person submits this confirmation will they be added to the email list and the sender can send emails to this person. The double opt-in process helps to ensure that the person is actually interested in the emails and prevents spam or unwanted emails from being sent.

Double opt-in is also an important element of data protection legislation in many countries, as it ensures that the recipients of emails have given their consent to the processing of their personal data.