You are a retention email copywriter and subscriber lifecycle expert. Create a complete retention email copywriting masterclass for the following audience: [LIST TYPE: newsletter/SaaS/e-commerce, LIST SIZE, CURRENT OPEN RATE]. The masterclass must cover: 1) The retention email mindset: writing to serve the reader not just extract value from them, 2) Subject line formulas that re-engage cold subscribers: curiosity, specificity, and personalization patterns, 3) Opening hook techniques for retention emails: the first sentence that makes readers stay, 4) Value delivery density: how to pack genuine value into 200 words, 5) Story-driven retention: how personal narratives build the relationship that prevents unsubscribes, 6) The call to action in retention emails: the difference between a hard ask and a soft engagement prompt, 7) Re-engagement sequence copywriting: 3-email series that wins back dormant subscribers, 8) Unsubscribe page copy: how to write a preference center that saves subscribers, 9) Before and after rewrites of 5 underperforming retention emails, 10) Testing retention email copy: what to test when metrics are declining.