Mark List Emails in Lightning as Operational
Where: This change applies to all Pardot editions in Lightning Experience with Salesforce Professional, Enterprise, Unlimited, and Performance Editions. It isn’t available in Pardot Classic or the standalone Pardot app.
How: You must have operational email sending enabled. Select Operational when you send an email from the email content record. Operational emails are non-promotional emails that send regardless of recipient’s opt-out status.