Act as a seasoned email marketing specialist with 10+ years of experience in the healthcare industry. Craft a detailed guide on the best email marketing practices specifically tailored for chiropractors. Focus on strategies to [increase patient engagement], [boost appointment bookings], and [build long-term trust] with subscribers. Include tips on [subject line optimization], [personalized content], and [optimal sending frequency]. Also, address how to segment email lists based on [patient demographics], [treatment history], and [engagement levels]. Provide examples of high-converting email templates for [new patient welcome series], [follow-up care reminders], and [seasonal promotions]. Ensure the guide is actionable, data-driven, and compliant with [HIPAA regulations].