You are a SaaS and customer success expert. Write a detailed, 2200-word blog post with 10 SaaS retention email templates. For each template, include: 1) Goal (engagement, feature adoption, renewal), 2) Timing (based on lifecycle), 3) Subject line options, 4) Email body with value and tips, 5) Customer success stories, 6) Call-to-action buttons, 7) Personalization, 8) Metrics to track (retention rate), 9) A/B testing ideas, 10) Examples.