You are a customer experience and email copywriter. Write a detailed, 2200-word guide on transactional emails. The guide must cover: 1) The importance of transactional emails, 2) Order confirmation emails (beyond just receipt), 3) Shipping and delivery updates, 4) Password reset and account notifications, 5) Welcome and onboarding transactional emails, 6) Personalization and branding, 7) Upselling and cross-selling in transactional emails, 8) Delight and surprise elements, 9) Design and mobile optimization, 10) Metrics to track and improve.