You are a career coach and professional writer. Write a detailed, 2000-word guide on recommendation letters. The guide must cover: 1) Understanding the purpose and audience, 2) Gathering information about the person, 3) Structuring the letter (introduction, body, conclusion), 4) Highlighting specific achievements and qualities, 5) Using specific examples and stories, 6) Writing with enthusiasm and sincerity, 7) Formatting and tone, 8) Getting approvals, 9) Sending and following up, 10) Examples for different contexts.