RustMailer is a self-hosted email middleware written in Rust that provides IMAP/SMTP functionality for developers. It offers multi-account email synchronization, template support, webhook integration, OAuth2 authentication, and a web-based admin interface. The tool is designed to help developers integrate email functionality into applications without building complex mail infrastructure from scratch. It includes features like email tracking, NATS integration, and VRL scripting for payload transformation. While the source code is publicly available, production use requires a commercial license after a 14-day free trial.