> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/puiusabin/bun-smtp/llms.txt
> Use this file to discover all available pages before exploring further.

# Introduction

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

# Welcome to bun-smtp

A fast SMTP/LMTP server library built natively on Bun, designed to be a drop-in replacement for `smtp-server` with significantly better performance.

## Why bun-smtp?

bun-smtp leverages Bun's native APIs like `Bun.listen()`, `socket.upgradeTLS()`, and `Bun.CryptoHasher` to deliver a high-performance SMTP server without relying on Node.js compatibility layers. If you're already using Bun, bun-smtp provides a seamless, fully-typed experience for handling email.

<CardGroup cols={2}>
  <Card title="Quickstart" icon="rocket" href="/quickstart">
    Get up and running in minutes with a minimal SMTP server
  </Card>

  <Card title="Authentication Guide" icon="lock" href="/guides/authentication">
    Learn how to implement SASL authentication (PLAIN, LOGIN, CRAM-MD5, XOAUTH2)
  </Card>

  <Card title="API Reference" icon="code" href="/api/smtp-server">
    Explore the complete API including all options and callbacks
  </Card>

  <Card title="Examples" icon="book-open" href="/examples/basic-server">
    See real-world examples of TLS, authentication, and message handling
  </Card>
</CardGroup>

## Key Features

<AccordionGroup>
  <Accordion title="Bun-native Performance" icon="gauge-high">
    Built directly on Bun's native APIs without Node.js compatibility overhead. Uses `Bun.listen()` for optimal socket handling and `Bun.CryptoHasher` for authentication.
  </Accordion>

  <Accordion title="Drop-in Replacement" icon="arrows-rotate">
    Same constructor options, callbacks, and event names as `smtp-server`. Migrate with minimal code changes while gaining significant performance improvements.
  </Accordion>

  <Accordion title="Full SMTP Support" icon="envelope">
    Implements the complete SMTP protocol including HELO/EHLO, MAIL FROM, RCPT TO, DATA, STARTTLS, LMTP mode, and extension commands like XCLIENT and XFORWARD.
  </Accordion>

  <Accordion title="SASL Authentication" icon="shield-halved">
    Built-in support for PLAIN, LOGIN, CRAM-MD5, and XOAUTH2 authentication methods with configurable options for insecure auth and required authentication.
  </Accordion>

  <Accordion title="TypeScript First" icon="code">
    Fully typed API with comprehensive TypeScript definitions for all options, callbacks, session data, and authentication objects.
  </Accordion>
</AccordionGroup>

## Quick Example

Here's a minimal SMTP server that accepts all messages:

```typescript theme={null}
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);
console.log("SMTP server listening on port 2525");
```

## System Requirements

<Info>
  bun-smtp requires **Bun 1.2.0 or higher**. Make sure you have Bun installed before getting started.
</Info>

Install Bun if you haven't already:

```bash theme={null}
curl -fsSL https://bun.sh/install | bash
```

## Community & Support

* **GitHub**: [puiusabin/bun-smtp](https://github.com/puiusabin/bun-smtp)
* **Issues**: [Report bugs or request features](https://github.com/puiusabin/bun-smtp/issues)
* **npm**: [bun-smtp on npm](https://www.npmjs.com/package/bun-smtp)

## License

bun-smtp is distributed under the MIT License. See the [LICENSE](https://github.com/puiusabin/bun-smtp/blob/main/LICENSE) file for details.