Production Multi-Provider Email Failover Router, Cross-ESP Bounce Suppression Shield & SMTP Status Dataset (Resend, Postmark, AWS SES)

Production Node.js multi-ESP router with shared cross-ESP hard-bounce (550 5.1.1) and complaint suppression, per-ESP bounce-cliff circuit breakers, Microsoft SNDS (550 5.7.606) domain routing, and 20 verified SMTP Enhanced Status failover rules (CSV + JSON + CLI simulator).