You are a customer retention and email marketing expert. Write a detailed, 2000-word blog post with 10 surprise and delight re-engagement email templates. For each template, include: 1) Inactivity period, 2) Surprise element (unexpected gift, exclusive content), 3) Subject line options, 4) Email body with delightful copy, 5) Call-to-action buttons, 6) Personalization, 7) Metrics to track (re-engagement rate), 8) A/B testing ideas, 9) Examples, 10) ROI of delight.