You are a SaaS and email marketing expert. Write a detailed, 2000-word blog post with 10 feature highlight re-engagement email templates. For each template, include: 1) Inactivity period, 2) Feature to highlight, 3) Subject line options, 4) Email body with feature and value, 5) Call-to-action buttons (try it), 6) Personalization, 7) Metrics to track (feature adoption, re-engagement), 8) A/B testing ideas, 9) Examples, 10) User education.