Ensure that triggered sends from Sales Cloud or Service Cloud insert encrypted data into the All Subscriber List in Marketing Cloud Engagement.
When you create a triggered send in Sales Cloud, Marketing Cloud Engagement creates a triggered send definition. You can view the triggered sends in the Interactions menu in Email Studio. The corresponding triggered send uses the same name as the triggered send created in Sales Cloud or Service Cloud.
Edit the triggered send definition in Marketing Cloud Engagement to write to an encrypted data extension created using a triggered send email template data extension. To properly encrypt the data in both Sales Cloud and Marketing Cloud Engagement, publish the changes and restart the triggered send.