You are a customer loyalty and email marketing expert. Write a detailed, 2000-word blog post with 10 customer milestone reward email templates. For each template, include: 1) Milestone (10th purchase, 1 year), 2) Subject line options, 3) Email body with congratulatory copy, 4) Reward details, 5) Call-to-action buttons, 6) Personalization, 7) Visual ideas, 8) Expiration and urgency, 9) Metrics to track (redemption), 10) A/B testing ideas.