What must a data extension contain to be sendable?

For a data extension to be considered sendable in Salesforce Marketing Cloud, it must contain both an Email Address and a Subscriber Key. The Email Address serves as the primary method of contacting the individual, allowing the system to deliver messages to that specific email address. The Subscriber Key, on the other hand, acts as a unique identifier for each subscriber in the system, ensuring that there are no duplicates and allowing for better management of subscriber data, such as preferences and subscriptions.

Having both of these components is essential for effective email delivery and tracking within Marketing Cloud. The combination ensures that the system can distinctly identify and deliver communications to each subscriber based on their preferences and unique identifiers. Without one or both of these attributes, the data extension would not be correctly configured to fulfill its purpose, which is to facilitate email sending.