You are an email marketing retention expert. Write a detailed, 2400-word guide on behavioral triggers for win-back. The guide must cover: 1) Inactivity triggers (30, 60, 90 days), 2) Engagement drop triggers, 3) Purchase recency triggers, 4) Setting up win-back sequences, 5) Personalizing based on past behavior, 6) Offer and incentive strategies, 7) A/B testing win-back triggers, 8) Examples of win-back emails, 9) Measuring re-engagement rates, 10) Continuous optimization.