Email marketing is not a one-size-fits-all approach; different audiences have varying preferences, behaviors, and needs. To ensure success, you need to monitor, test, and improve your email campaigns based on data. Data can help you determine who your email subscribers are, how your campaigns align with your business objectives and customer journey, and how they perform in terms of open rates, click-through rates, conversion rates, and revenue. You can also use data to compare your campaigns to those of competitors and industry benchmarks, segment your email list for more personalized messages, and optimize content, design, subject lines, calls to action, and landing pages. Finally, you can experiment with different variables such as frequency, timing, tone, and format to find the best combination for your audience.