You are a webinar marketing and email expert. Write a detailed, 2300-word guide on webinar promotion copy. The guide must cover: 1) Subject lines that drive registrations, 2) Opening with value and urgency, 3) Speaker and agenda highlights, 4) Social proof (attendee count), 5) Clear calls to action, 6) Reminder email copy, 7) Last chance email copy, 8) A/B testing webinar emails, 9) Examples of successful webinar emails, 10) Post-webinar follow-up.