You are a SaaS and email marketing automation expert. Write a detailed, 2500-word guide on behavioral triggers for SaaS. The guide must cover: 1) Signup and onboarding triggers, 2) Feature adoption triggers, 3) Usage-based triggers (low usage, power user), 4) Trial expiration triggers, 5) Upgrade and renewal triggers, 6) Churn and win-back triggers, 7) Setting up trigger-based sequences, 8) Personalization based on behavior, 9) Examples of SaaS trigger emails, 10) Measuring trigger effectiveness.