You are a travel industry and email marketing expert. Write a detailed, 2500-word guide on email for travel. The guide must cover: 1) Building an email list of travelers, 2) Welcome sequences for new subscribers, 3) Destination and travel inspiration emails, 4) Promotional emails for deals and packages, 5) Booking and confirmation emails, 6) Pre-trip and post-trip emails, 7) Loyalty and rewards program emails, 8) Re-engagement and win-back, 9) Integration with booking systems, 10) Metrics for travel (bookings, engagement).