What field in a sendable data extension relates to Subscribers on Subscriber Key?

The Customer_ID field in the Data Extension is the correct choice because it serves as a way to uniquely identify subscribers within the data extension in relation to the Subscriber Key. In Salesforce Marketing Cloud (SFMC), the Subscriber Key is a primary identifier for each subscriber across different data extensions and is critical for managing and tracking subscriber data effectively.

When designing data extensions, it is essential for the primary key in that data extension to align with the Subscriber Key in order to maintain relational integrity and ensure that any interactions, such as sending emails or managing subscriber preferences, can be accurately connected to the right subscriber. The Customer_ID field thus fulfills this role, allowing marketers to correlate the information in the data extension directly with specific subscribers in the subscriber management system.

Other options provided do not serve the same purpose: while the Subscriber ID in a System Data View Table might offer insights into subscriber behavior, it does not function as a direct field for identification in a sendable data extension. The Email Address Profile Attribute refers specifically to the email address associated with a profile but does not match the Subscriber Key conceptually. Lastly, the Email_Address field in the Data Extension, while relevant to a subscriber's contact information, does not provide a unique identifier; rather, the Subscriber Key