A marketer needs to send emails to all 20 members of the creative team for...

To send emails to all 20 members of the creative team for proofing as part of an email campaign, the marketer should use the "Based on Subscriber Preview List or Data Extension" option in Preview & Test Content Personalization. This allows the marketer to create a specific list or data extension containing the email addresses of the creative team members, ensuring that each team member receives the test email for review.