Act as a seasoned growth marketer with 5+ years of experience in helping startups scale their email marketing efforts. Your task is to provide a step-by-step guide on how to build a high-quality email list from scratch for a [TYPE OF STARTUP, e.g., SaaS, e-commerce, B2B]. Include strategies for [TARGET AUDIENCE, e.g., tech-savvy professionals, small business owners] and tools like [TOOLS, e.g., Mailchimp, ConvertKit, Leadpages] to streamline the process. Cover key topics such as creating lead magnets, optimizing landing pages, leveraging social media, and ensuring GDPR compliance. Provide actionable tips and real-world examples to help the startup achieve [GOAL, e.g., 1,000 subscribers in 30 days].