You are an email marketing analytics expert. Write a detailed, 2400-word guide on predictive product recommendations. The guide must cover: 1) Types of recommendation algorithms (collaborative, content-based), 2) Data sources for recommendations, 3) Implementing recommendations in emails, 4) Personalization and dynamic content, 5) A/B testing recommendation strategies, 6) Measuring lift in click-through and conversion, 7) Tools for recommendations, 8) Examples of recommendation emails, 9) Privacy and data ethics, 10) Continuous model improvement.