The major difference between opt-in and opt-out is the way in which customers or users are treated by a system and the type of input required of them. An opt-in system is one in which a person needs to actively indicate interest or a desire to be a part of something. In contrast, an opt-out arrangement makes users part of a system, and provides them with the opportunity to remove themselves from it. With regard to technology, the way in which the initial communication in opt-in and opt-out methods is handled is different, with more options available up front for the former.
One of the biggest ways in which an opt-in and opt-out system differ is how a user initially interacts with each of them. An opt-in agreement is one in which someone has to actively select that he or she wants to be a part of a newsletter or other opportunity. This requires some forethought on the behalf of developers or coders making this type of option, as the choice needs to be clear to a user.
An opt-in system is typically designed to be approachable and provide as much information as possible. Using an opt-in method requires development of an interface that clearly presents the option. Contact information needs to be provided by someone interested in information through this system, and it can simply be added to a list of opt-in registrations.
While both systems are means by which information can be distributed to others, the way in which people become a part of them is quite different. In an opt-out arrangement, someone is automatically qualified as a contact and they become registered through another system. This can occur through sale of contact data, though it is often used as a means of ongoing communication after a sale or other service.
From a technological standpoint, an opt-out system can be fairly easy to create. Data is used from another source to populate a list of individuals who are a part of this service. It is up to users to then indicate that they no longer wish to be part of a mailing list or other program. Some method needs to be provided for them to opt-out of the arrangement. This can be somewhat complicated, but usually involves a link or other simple indicator that sends a notice to remove someone's information from a list.
It is typically best for a service to use a method that is a combination of an opt-in and opt-out agreement. The initial terms for contact can be established through opt-in features, with additional opportunities to opt-out at a later time. When someone does wish to opt-out, options can be provided to continue receiving some information while eliminating features that were not desired. A combination of opt-in and opt-out features can require the use of multiple tables and lists to maintain various opportunities. Doing so, however, allows people to control the frequency or scale of future communication.