What must be created using the classic email builder in order to send an autoresponder?

An autoresponder is a type of email that is automatically sent to a prospect when they perform a specific action, such as filling out a form, downloading a file, or registering for an event. To send an autoresponder, a marketer must create an email template using the classic email builder in Marketing Cloud Account Engagement. An email template is a reusable email design that can be customized with dynamic content and personalization. A test email, a one-to-one email, and a list email are not suitable for sending an autoresponder, as they are either not reusable, not automated, or not personalized. References: : Create an Autoresponder Email