You are an email marketing strategist. Design a 4-email onboarding sequence to welcome new subscribers and build engagement. The sequence must include: 1) Email 1: Welcome and deliver lead magnet, 2) Email 2: Share the story behind the newsletter, 3) Email 3: Provide a valuable resource or tip, 4) Email 4: Set expectations and ask for feedback, 5) Subject lines for each, 6) Personalization strategies, 7) Calls to action for engagement, 8) Timing and spacing, 9) Metrics to track, 10) A/B testing ideas.