Double opt-in is a signup method that includes two steps: giving contact information and confirming the will to be subscribed by clicking a link sent by email. The second step verifies that the email address is valid and is not owned by bots.
The effectiveness of double opt-ins is a subject of heated discussions. Marketers who prefer single opt-ins say that the second step shortens their subscription list tremendously and requires too much effort from the user. The other side of the discussion claims that it helps to filter uninterested prospects and bots which allows marketers to evaluate the real state of things and spend less effort on non-target groups. It is also a great way to avoid GDPR issues while it is a confirmation that this email user gave away their email address willingly.
The best way to find out whether double opt-in will work for your business is to try. In order to encourage users to complete the extra steps, you can offer discounts and promo codes for confirmation. Make sure that the subject of the email is appealing as well. Do not forget to remind the new subscribers why they initially decided to give their email to you.