Act as a seasoned email marketing strategist with 7+ years of experience working with tech startups. Craft a detailed guide on the best practices for email marketing tailored specifically for [tech startups in the SaaS industry]. Cover essential topics such as [subject line optimization], [personalization techniques], and [conversion-driven CTAs]. Include real-world examples of successful campaigns from startups like [Company X] or [Company Y], and explain how they leveraged segmentation and A/B testing to improve open rates and click-through rates. Also, address common pitfalls to avoid, such as [overloading subscribers with emails] or [failing to optimize for mobile]. Provide actionable tips for building a high-quality subscriber list and maintaining engagement over time.