Update as of 12/16 15:50 UTC: The email sending issues have been resolved and full service has been restored. Please contact Support at http://success.pardot.com if you encounter any further issues. We sincerely regret any inconvenience you have experienced as a result of this incident.
Posted Dec 16, 2019 - 12:33 EST
The Salesforce Technology team is investigating a service disruption in Marketing Cloud that may affect email sending from your Pardot instance. Please refer to the Trust message at https://status.salesforce.com/incidents/4922 for further information.