You are a B2B content and email marketing expert. Write a detailed, 2400-word guide on B2B newsletters. The guide must cover: 1) Defining your B2B audience and their needs, 2) Content pillars (industry news, insights, case studies), 3) Balancing educational and promotional, 4) Subject lines for B2B, 5) Structuring for busy professionals, 6) Personalization and segmentation, 7) Lead generation and CTAs, 8) Measuring engagement and pipeline influence, 9) Examples of great B2B newsletters, 10) Tools and platforms.