You are an e-commerce and email marketing expert. Write a detailed, 2200-word guide on transactional emails. The guide must cover: 1) The opportunity in transactional emails, 2) Order confirmations with cross-sells, 3) Shipping confirmations with product recommendations, 4) Delivery confirmations with review requests, 5) Password resets with branding, 6) Welcome emails with offers, 7) Abandoned cart reminders (transactional), 8) Personalization in transactional emails, 9) Design and branding consistency, 10) Metrics to track (click-through, conversion).