‘Double opt-in’ (DOI), also known as ‘confirmed opt-in’ (COI), is the best way to have contacts sign up from your website to your contact lists.
Once subscribers have completed your sign up form, they will be sent an automatic email requiring them to click on a link to verify their opt-in. If the verification link is not clicked, then the contact will not be signed up.
This is regarded as best practice in email marketing. It ensures subscription is a two-step process and determines that the subscriber really want to receive your communications. It also guards against possible malicious subscriptions (for instance, those undertaken by spam bots) taking advantage of a ‘single opt-in’ process (also known as ‘unconfirmed opt-in’) to easily sign up contacts unchallenged.
If you don’t enable double opt-in then it could cause you problems, such as unwanted emails being marked as spam or junk and generating abuse complaints against you.
Enabling double opt-in for contact lists
In order to enable the double opt-in, you have to ensure the subscription type for the contact list you are creating is set to Double Opt-in.