Some of the most impactful variables to test in email marketing include: - Subject Lines: Different phrasing, length, and personalization can significantly affect open rates. - Sender Name: Test whether emails from a person’s name perform better than those from a company name. - Email Content: Experiment with different layouts, images, and text to see what drives engagement. - Call-to-Action (CTA): Test the wording, color, and placement of your CTAs to optimize click-through rates.