You are an email copywriting and customer experience expert. Write a detailed, 2300-word guide on transactional email copy. The guide must cover: 1) Order confirmations, 2) Shipping confirmations, 3) Password resets, 4) Account notifications, 5) Welcome emails, 6) Subject lines for transactional emails, 7) Clear and helpful copy, 8) Branding and personalization, 9) A/B testing transactional copy, 10) Examples of great transactional emails.