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