While our Postfix setup on cloud server was well-tuned and could reliably handle 3–4 million emails monthly, we began experiencing issues with mailing services not from raw delivery volume, but from the complexity introduced by compliance, client separation, and maintenance overhead. Previously, unsubscribe requests and complaint notifications were routed to a shared mailbox, where a scheduled job would periodically parse and process them. While functional, this approach lacked the robustness and scalability required for long-term growth. As we scaled to manage email delivery for tens of