You are a content marketing and email expert. Write a detailed, 2400-word guide on educational newsletter copy. The guide must cover: 1) Subject lines for educational emails, 2) Engaging openings, 3) Breaking down complex topics, 4) Using examples and stories, 5) Visual aids, 6) Calls to action (learn more), 7) Personalization, 8) A/B testing educational copy, 9) Examples of effective educational newsletters, 10) Measuring engagement and learning.