You are a growth and referral marketing expert. Write a detailed, 2000-word blog post with 10 referral program email templates. For each template, include: 1) Email type (invitation, reminder, reward notification), 2) Subject line options, 3) Email body with persuasive copy, 4) Incentive details for both parties, 5) Referral link and sharing options, 6) Social proof (friends already joined), 7) Call-to-action buttons, 8) Timing and triggers, 9) Metrics to track (referral rate, conversion), 10) A/B testing ideas.