Design a Global Marketing Email Platform

Design a marketing email system for a large consumer marketplace. The business wants to run campaigns that may send 2-3 marketing emails within a 15-minute delivery window. The system must support users across multiple time zones and allow marketers to define campaigns, audiences, templates, and send schedules. Key requirements: - schedule delivery correctly for users in different time zones - support A/B testing across different email variants - track whether an email was accepted, delivered, bounced, opened, clicked, unsubscribed, and whether it led to a downstream conversion - expose metrics so marketers can compare experiment performance and overall campaign effectiveness - remain reliable even when email providers throttle requests or return transient failures Describe the architecture, core data model, scheduling strategy, delivery pipeline, experimentation logic, and tracking and analytics flow.