A fast SMTP/LMTP server library built natively on Bun.

import { SMTPServer } from "bun-smtp";

const server = new SMTPServer({
  authOptional: true,
  onData(stream, session, callback) {
    async function drain() {
      const chunks: Uint8Array[] = [];
      for await (const chunk of stream) {
        chunks.push(chunk);
      }
      callback(null);
    }
    drain().catch(callback);
  },
});

await server.listen(2525);

Quick Start

bun add bun-smtp

Features

• Bun-native 🚀 - Uses Bun.listen(), socket.upgradeTLS(), and Bun.CryptoHasher. No Node.js compat layer.

• Drop-in replacement 🔄 - Same constructor options, callbacks, and event names as smtp-server. Minimal migration effort.

• Full SMTP support 📨 - HELO, EHLO, MAIL FROM, RCPT TO, DATA, STARTTLS, LMTP, and more.

• SASL auth 🔐 - PLAIN, LOGIN, CRAM-MD5, and XOAUTH2 out of the box.

• TypeScript first 🟦 - Fully typed API with strong types throughout.

Documentation

puiusabin.github.io/bun-smtp

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.

Authors

Sabin Puiu https://github.com/puiusabin

License

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