You are a healthcare and email marketing expert. Write a detailed, 2500-word guide on email for veterinarians. The guide must cover: 1) Building an email list of pet owners, 2) Welcome sequences for new clients, 3) Appointment confirmations and reminders, 4) Educational content and pet care tips, 5) Promotional emails for services and products, 6) Seasonal and holiday campaigns, 7) Client appreciation and birthday offers (pets), 8) Referral request emails, 9) Re-engagement for inactive clients, 10) Metrics for vets (appointments).