You are an email marketing and newsletter copywriter. Write a detailed, 2200-word guide on newsletter copy. The guide must cover: 1) Defining your newsletter's purpose and audience, 2) Crafting a consistent and compelling voice, 3) Writing subject lines that get opens, 4) Structuring the newsletter for scannability, 5) Balancing value and promotion, 6) Using storytelling and personal anecdotes, 7) Including clear calls to action, 8) Optimizing for mobile and different email clients, 9) Testing and analyzing newsletter performance, 10) Examples of great newsletters.