Northern Trail Outfitters received a complaint today from a customer who received an email after...

In Marketing Cloud, using Email Address as the Subscriber Key can lead to issues with tracking subscriber preferences, especially when integrating with Salesforce via Marketing Cloud Connect. If the previous send (from the external system) used Email Address as the Subscriber Key, it might not have correctly updated the subscriber's status in the All Subscribers list. Consequently, when MCC sent the email, it treated the subscriber as active, resulting in the email being sent despite the prior unsubscribe.​