You are a video marketing and email expert. Write a detailed, 2300-word guide on video emails. The guide must cover: 1) Why video works in email (engagement, click-through), 2) Types of video emails (product demos, tutorials, testimonials, personal messages), 3) Technical implementation (GIFs, thumbnails, embedded video), 4) Best practices for video thumbnails, 5) Hosting and delivery considerations, 6) Mobile optimization, 7) A/B testing video vs. text, 8) Metrics to track (play rate, click rate), 9) Tools for creating video emails, 10) Examples of effective video emails.