Configuring Newsletter in the backend is required if you want to create newsletters for your site. Newletters are important documents to inform clients regularly about your store’s activities particularly as promotions, discounts or loyalty programs. Thus, setting up newsletters is the perfect step for customer loyalty.
Within the configuration, you can give a confirmation link that the customers need to click on to complete the subcription process. The process that requires customers to take a secondary step to verify the suscription is called the double opt-in1 method. Applying this method will reduce the spam to your newsletters.
To configure the newsletters, follow this tutorial:
Stores > Settings > Configuration.
Subcription Optionssection, you need to do:
Need to Confirmfield.
Allow Guest Subscriptionsto Yes.
Save Configto complete.
Ref: Magento 2 User Guide
It comes to the end of tutorial: How to configure Newsletters in Magento 2.