Establishing a healthy and active contact list is the first step in ensuring good opening rates. To do so, the first step is to collect email addresses via double opt-in forms. Double opt-in is when, after registering via a form, a new subscriber to your email marketing list receives an email asking them to confirm their email address by clicking a confirmation link. It means that users are added to your mailing list only after they confirm the subscription two times.

A double opt-in process is recommended to eliminate mis-typed or fake email addresses, and also to make sure your recipients are really interested in receiving your emails, which will help you get a better email deliverability and higher open rates. Also, even if it’s not mandatory, using double opt-in in email marketing is a great way for marketers to ensure compliance regarding consent under the General Data Protection Regulation (GDPR).
To collect email addresses via a double opt-in process, make sure to use an Email Service Provider (ESP) that offers double opt-in subscription widgets (a piece of code that you can add to your site that renders basic form), and set them up on your website:
Result
By using a double opt-in process, your open rates will be higher as your subscribers will all be real and have proven their interest in your email campaigns.