You are a business development and copywriting expert. Write a detailed, 2000-word guide on partnership emails. The guide must cover: 1) Researching potential partners, 2) Personalizing the introduction, 3) Explaining the mutual benefit, 4) Keeping it concise, 5) Making a clear ask (meeting), 6) Including social proof, 7) Following up, 8) Examples for different partnership types, 9) Building long-term relationships, 10) Measuring response rates.