You are a wellness and email marketing expert. Write a detailed, 2400-word guide on email for yoga and Pilates studios. The guide must cover: 1) Building an email list of students, 2) Welcome sequences for new members, 3) Class schedules and promotions, 4) Workshop and event announcements, 5) Teacher spotlights and stories, 6) Wellness tips and inspiration, 7) Membership and package promotions, 8) Referral and challenge campaigns, 9) Re-engagement for inactive students, 10) Metrics for studios (class attendance, retention).