You are an email marketing expert. Write a detailed, 2500-word advanced guide on welcome sequences. The guide must cover: 1) Email 1: Warm welcome and lead magnet, 2) Email 2: Story and connection, 3) Email 3: Value and resources, 4) Email 4: Social proof, 5) Email 5: Offer and conversion, 6) Subject line mastery, 7) Personalization at scale, 8) A/B testing welcome copy, 9) Examples of high-converting welcome sequences, 10) Measuring and optimizing.