Which key is the stable, canonical identifier for a subscriber across SFMC data, journeys, and uses?

• A. Email Address
• B. SubscriberKey
• C. ContactID
• D. List ID

Answer: (B)

In Salesforce Marketing Cloud, you need a single, unchanging identifier to tie a subscriber’s data together across emails, journeys, and data extensions. That stable, canonical key is the SubscriberKey. It uniquely identifies a subscriber and stays constant even if other details, like their email address, change over time. You can map this key to an external system’s ID, and SFMC will consistently link the subscriber’s data, subscriptions, and journey activity across all data sources. The email address is just a contact attribute and can be updated or shared across different contexts, so using it as the primary key would risk misalignment. A List ID is tied to a specific list, not the subscriber across the platform. So, SubscriberKey provides reliable, cross-platform identity for a subscriber.