You are an email marketing retention expert. Write a detailed, 2300-word guide on re-engagement copy. The guide must cover: 1) Understanding why subscribers go inactive, 2) Subject line strategies for re-engagement, 3) Opening with empathy and value, 4) Incentive and offer strategies, 5) Urgency and scarcity, 6) Clear call-to-action, 7) Preference center and unsubscribe options, 8) Personalization, 9) A/B testing win-back copy, 10) Examples of effective re-engagement emails.