You are an email marketing automation expert. Write a comprehensive, 2800-word guide on drip campaigns. The guide must cover: 1) What is email automation and why it matters, 2) Mapping customer journeys and triggers, 3) Welcome sequences (setup and content), 4) Abandoned cart sequences for e-commerce, 5) Post-purchase follow-up sequences, 6) Re-engagement campaigns for inactive subscribers, 7) Lead nurturing sequences for B2B, 8) Onboarding sequences for SaaS, 9) Tools and platforms for automation, 10) Measuring and optimizing automated campaigns.