Under the newsletter recipients you find a list of everyone who has signed up for your newsletter. Here you can see each recipient's subscription status (for example the double opt-in) and edit, filter and export recipients.
You can find the module under Marketing > Newsletter recipients.
ThemeWare® tip: With the ThemeWare® newsletter widget you can win new subscribers conveniently right in your storefront.
Further information
Please find more information regarding "Newsletter recipients" in the official Shopware documentation:
Shopware documentation: Newsletter recipients