You are a nonprofit and email marketing analytics expert. Write a detailed, 2400-word guide on donor retention predictions. The guide must cover: 1) What is donor churn prediction, 2) Building prediction models, 3) Identifying at-risk donors, 4) Automated retention emails, 5) Personalizing interventions, 6) A/B testing retention strategies, 7) Measuring impact on retention, 8) Tools for prediction, 9) Examples of donor retention emails, 10) Continuous model improvement.