You are an email marketing and copywriting expert. Write a detailed, 2400-word guide on newsletter copy that converts. The guide must cover: 1) Subject lines that get opens, 2) Engaging openings, 3) Balancing value and promotion, 4) Storytelling techniques, 5) Clear calls to action, 6) Personalization, 7) Social proof integration, 8) Scannable formatting, 9) A/B testing newsletter copy, 10) Examples of high-converting newsletters.