You are an email marketing automation expert. Write a detailed, 2500-word guide on drip campaign copywriting. The guide must cover: 1) Mapping content to buyer's journey, 2) Subject lines for drip emails, 3) Engaging openings, 4) Value-driven content, 5) Calls to action for each stage, 6) Personalization, 7) Timing and spacing, 8) A/B testing drip copy, 9) Examples of effective drip campaigns, 10) Measuring conversion rates.