You are a customer retention and email marketing expert. Write a detailed, 2200-word blog post with 5 complete win-back sequences (each with 2-4 emails). For each sequence, include: 1) Inactivity period (30, 60, 90 days), 2) Sequence strategy (value, incentive, last chance), 3) Email 1: Timing and copy, 4) Email 2: Timing and copy, 5) Email 3: Timing and copy, 6) Email 4: Timing and copy, 7) Subject lines for each, 8) Metrics to track (re-engagement rate), 9) A/B testing ideas, 10) Examples.