simplesmtp: Simple SMTP Server and Client Module

Common errors

• TypeError: req.pipe is not a function

  cause This error likely occurs when running `simplesmtp` on Node.js versions v0.12 or newer. The module was written for older Node.js streams and is incompatible with modern stream APIs.
  fix This package is fundamentally incompatible with modern Node.js. Replace `simplesmtp` with a contemporary, actively maintained SMTP library like `smtp-server`.

• Error [ERR_REQUIRE_ESM]: require() of ES Module ... is not supported.

  cause You are attempting to use the CommonJS `require()` function in an ES Module context, or trying to `import` a CommonJS module in a way that is not directly supported by Node.js, possibly due to `type: module` in `package.json`.
  fix This package is strictly CommonJS. If your project is an ESM project, you will need to wrap the `require` call or, preferably, switch to a modern, ESM-compatible SMTP library. For this specific package, ensure your environment is CommonJS compatible (e.g., remove `"type": "module"` from `package.json` if possible, or use a CommonJS entry point).

• Cannot find module 'simplesmtp'

  cause The `simplesmtp` package has not been installed, or there is a typo in the `require()` path.
  fix Run `npm install simplesmtp` to add the package to your project dependencies. Verify the spelling of the module name in your `require()` statement.

Warnings

• breaking This module is officially deprecated and no longer maintained. It does not use Node.js v0.10 streams and is explicitly stated to have a 'rocky future' with Node.js v0.12+. Using it with modern Node.js versions (v0.12+) will likely result in runtime errors related to stream APIs or other breaking changes.
  Fix: Migrate to `smtp-server` for SMTP server functionality or `smtp-connection` for SMTP client functionality. For full-featured servers, consider `Haraka`.
• deprecated Security vulnerabilities in this abandoned package will not be patched. Using `simplesmtp` in production environments or with sensitive data is highly discouraged due to the lack of security updates and potential for undiscovered exploits.
  Fix: Immediately replace `simplesmtp` with actively maintained and secure alternatives (`smtp-server`, `smtp-connection`, `Haraka`). Regularly review security advisories for your chosen alternatives.
• gotcha Compatibility with Node.js v0.6 requires using `simplesmtp` v0.2.7. Later versions (v0.3.x) are designed for Node.js v0.8+.
  Fix: For Node.js v0.6, explicitly install `simplesmtp@0.2.7`. For Node.js v0.8+, use `simplesmtp@0.3.x`, but be aware of its overall deprecation.
• breaking The module is CommonJS-only. Attempting to use ESM `import` statements will result in a runtime error.
  Fix: Always use `const simplesmtp = require('simplesmtp');` for importing this module.

Install

• npm install simplesmtp npm
• yarn add simplesmtp yarn
• pnpm add simplesmtp pnpm

Imports

• simplesmtp
  wrong:

  import simplesmtp from 'simplesmtp';

  correct:

  const simplesmtp = require('simplesmtp');

  This module is CommonJS-only, designed for older Node.js environments. ES Modules (ESM) import syntax will not work.
• createSimpleServer
  wrong:

  import { createSimpleServer } from 'simplesmtp';

  correct:

  const simplesmtp = require('simplesmtp');
  simplesmtp.createSimpleServer(/* options */, requestListener);

  The `createSimpleServer` function is a property of the main `simplesmtp` module export, not a named export. Ensure you import the entire module first.
• createServer
  wrong:

  const server = require('simplesmtp').createServer();

  correct:

  const simplesmtp = require('simplesmtp');
  const server = simplesmtp.createServer(/* options */);

  While `require('simplesmtp').createServer()` might work, the idiomatic pattern for this library is to import the main module first, then access its methods for clarity and consistency.

Quickstart

This quickstart sets up a basic `simplesmtp` server that listens on port 2525 (or `SMTP_PORT` if set), logs incoming email metadata, pipes the email body to standard output, and then accepts the message.

const simplesmtp = require('simplesmtp');

const PORT = process.env.SMTP_PORT || 2525;

simplesmtp.createSimpleServer({
  SMTPBanner: "My Test SMTP Server",
  debug: true
}, function(req) {
  console.log(`[simplesmtp] New message from: ${req.from}`);
  console.log(`[simplesmtp] To: ${req.to.join(', ')}`);
  console.log(`[simplesmtp] Host: ${req.host}`);
  console.log(`[simplesmtp] Client IP: ${req.remoteAddress}`);

  // Pipe the incoming email data to stdout
  console.log('\n--- Email Body Start ---');
  req.pipe(process.stdout);
  req.on('end', () => {
    console.log('\n--- Email Body End ---');
    // Accept the message after processing
    req.accept();
    console.log(`[simplesmtp] Message accepted from ${req.from}`);
  });
}).listen(PORT, function() {
  console.log(`[simplesmtp] Simple SMTP server listening on port ${PORT}`);
  console.log('Send an email to this server (e.g., via telnet: `telnet localhost 2525`, then SMTP commands like `MAIL FROM:<test@example.com>`, `RCPT TO:<recipient@example.com>`, `DATA`, `Subject: Test\n\nHello world!\n.`)');
});