Hi there, I have launched a monthly online event for which I am collecting payment via Shopify. For my normal mailing list, I prefer the double opt-in but for the subscribers who sign up for this event (and agree to be added to my mailing list), a double optin is a cumbersome additional step. They are committed ofcourse because they have paid the fee and are expecting at least 3 emails related to the event they signed up for. What is the best practice for this segment of people?