You are a customer retention and email marketing expert. Write a detailed, 2000-word blog post with 10 free resource-based re-engagement email templates. For each template, include: 1) Inactivity period, 2) Resource type (ebook, guide, template), 3) Subject line options, 4) Email body with resource offer, 5) Call-to-action buttons (download), 6) Personalization, 7) Metrics to track (download rate, re-engagement), 8) A/B testing ideas, 9) Examples, 10) Content strategy.