I haven’t tested this but I’d approach this via the activity that is being associated with the contact when you’re logging an email to the record. You should be able to reference this email via the Email subject (or any other suiting email-related) activity property:
Hi @karstenkoehler. This workflow is exactly what I’m looking for, however, I need contacts to enroll multiple times. Any ideas on how to re-enroll contacts if they meet the criteria again? Since the activities are available for re-enrollment, how would you get contacts through the workflow multiple times? Thanks!