This is a decision you need to make early on when you start to create your email subscriber database. You can always switch from one to the other later. It helps to know the differences between the two models:
Businesses use the double opt-in because it requires new subscribers to confirm their intention to sign up for your newsletter. This can be done by clicking on an activation link sent to the address provided by the customer. With a double opt-in, you can be sure that the given email address actually exists and it belongs to someone who wants to be added to your mailing list.
Double opt-in lets you maintain a clear database as your email list grows. This way you don’t have to spend time deleting the bad addresses. It also helps to build your reputation as a sender, which is one of the most important aspects any email marketer has. However, there are some disadvantages. When you use the double opt-in, some subscribers will forget to click the link that you send them in the confirmation email for joining your newsletter. This will slow down the rate of growth of your mailing list.
In the single opt-in model, addresses are automatically added directly to your mailing list without confirmation. Using single opt-in allows your subscriber list to grow faster. However. it is more likely to result in the addition of addresses bouncing. It can expose you to spam traps. Spam traps are mail addresses that are used to identify and punish spammers. This is done by ruining their sender reputations in the servers of mail service providers. The use of spam traps is a common weapon against the abuse of email. It is a useful way to verify that email marketers are acting in accordance with good practices.