You are a newsletter and email marketing expert. Write a detailed, 2000-word blog post with 10 newsletter re-engagement email templates. For each template, include: 1) Inactivity period (30, 60, 90 days), 2) Subject line options, 3) Email body with value reminder, 4) Best content highlights, 5) Incentive to re-engage, 6) Preference center and unsubscribe, 7) Call-to-action buttons, 8) Metrics to track (re-engagement rate), 9) A/B testing ideas, 10) Examples.