The **simplesmtp** package provides a Node.js library for building custom SMTP servers and clients, including support for authentication, TLS, and connection pooling. It lets developers create lightweight inbound servers or send email programmatically, but the module is now deprecated in favor of smtp‑server, smtp‑connection or full‑featured solutions like Haraka. It’s aimed at developers needing a simple SMTP implementation for testing or integration within Node applications.