The foundations of current contact databases were shaken with the new GDPR rules. Every competent marketer is looking for ways to find out how and when to address their target group and gain the most valuable thing a company can have and that is to contacts that they can communicate with.
These are the forms that pop up from sides or upwards or downwards. They act however you want them. After sending them they can send an email, a notification or save the contact directly. Everything in accordance with GDPR. They can do even more via interconnected automatizations.
Double opt-in is a shortcut used for verifying the owner of an email address that your customers give you by filling out forms on your web pages.