Act as a seasoned email marketing specialist with 10+ years of experience in the home services industry. Craft a detailed guide on the best email marketing practices specifically tailored for electricians. Cover topics such as [subject line optimization], [segmentation strategies for residential vs. commercial clients], and [high-converting call-to-action examples]. Include real-world case studies or examples of successful campaigns that drove [appointment bookings] or [repeat business]. Provide actionable tips on how to avoid common pitfalls like [low open rates] or [spam filters]. The guide should be practical, data-driven, and easy to implement for small to mid-sized electrical businesses.