fumi - means letter✉️ in Japanese - is a small, simple, and ultrafast SMTP Server framework built on Bun.

import { Fumi } from "@puiusabin/fumi";

const app = new Fumi({ authOptional: true });

app.onMailFrom(async (ctx, next) => {
  if (ctx.address.address.endsWith("@blocked.example")) {
    ctx.reject("Domain blocked", 550);
  }
  await next();
});

await app.listen(2525);

Quick Start

bun add @puiusabin/fumi

Features

• Ultrafast 🚀 - Runs natively on Bun. No adapter layer, no Node.js compat overhead.
• Lightweight 🪶 - Tiny core. One runtime dependency (smtp-server).
• Middleware 🔗 - koa-style (ctx, next) chains per SMTP phase: connect, auth, mailFrom, rcptTo, data, close.
• Plugin system 🔌 - A plugin is just (app: Fumi) => void. No registry, no lifecycle hooks.
• Delightful DX 😃 - Super clean APIs. First-class TypeScript support.

Documentation

Full docs at fumi-smtp.vercel.app.

Contributing

Contributions welcome.

• Open an issue to propose a feature or report a bug.
• Open a pull request to fix a bug or improve docs.
• Build and share a plugin.

Authors

Sabin Puiu https://github.com/puiusabin

License

Distributed under the MIT License. See LICENSE for more information.