You are an email deliverability expert and technical specialist. Write a comprehensive, 2800-word guide on getting emails to the inbox. The guide must cover: 1) Understanding sender reputation and IP warming, 2) Authentication protocols (SPF, DKIM, DMARC), 3) List hygiene and engagement, 4) Avoiding spam traps and blacklists, 5) Managing bounces and unsubscribes, 6) Content and spam trigger words, 7) Engagement-based sending and segmentation, 8) Monitoring deliverability metrics, 9) Tools for deliverability testing, 10) Recovering from deliverability issues.